[generic_config_updater] Logging (#1864)

#### What I did
Add some logs to generic_updater

#### How I did it

#### How to verify it

#### Previous command output (if the output of a command-line utility has changed)

#### New command output (if the output of a command-line utility has changed)
Empty patch
```
admin@vlab-01:~$ sudo config apply-patch empty.json-patch 
Patch Applier: Patch application starting.
Patch Applier: Patch: []
Patch Applier: Validating patch is not making changes to tables without YANG models.
Patch Applier: Getting current config db.
Patch Applier: Simulating the target full config after applying the patch.
Patch Applier: Validating target config according to YANG models.
... [logs from sonic-yang-mgmt framework]
Patch Applier: Sorting patch updates.
Patch Applier: The patch was sorted into 0 changes.
Patch Applier: Applying changes in order.
Patch Applier: Verifying patch updates are reflected on ConfigDB.
Patch Applier: Patch application completed.
Patch applied successfully.
admin@vlab-01:~$ 
```

Single change patch
```
admin@vlab-01:~$ sudo config apply-patch dhcp_add.json-patch 
Patch Applier: Patch application starting.
Patch Applier: Patch: [{"op": "add", "path": "/VLAN/Vlan1000/dhcp_servers/4", "value": "192.0.0.5"}]
Patch Applier: Validating patch is not making changes to tables without YANG models.
Patch Applier: Getting current config db.
Patch Applier: Simulating the target full config after applying the patch.
Patch Applier: Validating target config according to YANG models.
... [logs from sonic-yang-mgmt framework]
Patch Applier: The patch was sorted into 1 change:
Patch Applier:   * [{"op": "add", "path": "/VLAN/Vlan1000/dhcp_servers/4", "value": "192.0.0.5"}]
Patch Applier: Applying changes in order.
Failed to apply patch
Usage: config apply-patch [OPTIONS] PATCH_FILE_PATH
Try "config apply-patch -h" for help.

Error: ChangeApplier.apply(change) is not implemented yet
admin@vlab-01:~$ 
```

Multi change patch:
```
admin@vlab-01:~$ sudo config apply-patch update_lanes.json-patch 
Patch Applier: Patch application starting.
Patch Applier: Patch: [{"op": "replace", "path": "/PORT/Ethernet100/lanes", "value": "121,122,123"}]
Patch Applier: Validating patch is not making changes to tables without YANG models.
Patch Applier: Getting current config db.
Patch Applier: Simulating the target full config after applying the patch.
Patch Applier: Validating target config according to YANG models.
... [logs from sonic-yang-mgmt framework]
Patch Applier: Sorting patch updates.
... [logs from sonic-yang-mgmt framework]
Patch Applier: The patch was sorted into 2 changes:
Patch Applier:   * [{"op": "remove", "path": "/PORT/Ethernet100"}]
Patch Applier:   * [{"op": "add", "path": "/PORT/Ethernet100", "value": {"alias": "fortyGigE0/100", "description": "fortyGigE0/100", "index": "25", "lanes": "121,122,123", "mtu": "9100", "pfc_asym": "off", "speed": "40000", "tpid": "0x8100"}}]
Patch Applier: Applying changes in order.
Failed to apply patch
Usage: config apply-patch [OPTIONS] PATCH_FILE_PATH
Try "config apply-patch -h" for help.

Error: ChangeApplier.apply(change) is not implemented yet
admin@vlab-01:~$ 
```

generic_config_updater/generic_updater.py

@@ -2,7 +2,7 @@
 import os
 from enum import Enum
 from .gu_common import GenericConfigUpdaterError, ConfigWrapper, \
-                       DryRunConfigWrapper, PatchWrapper
+                       DryRunConfigWrapper, PatchWrapper, genericUpdaterLogging
 from .patch_sorter import PatchSorter
 
 CHECKPOINTS_DIR = "/etc/sonic/checkpoints"
@@ -32,38 +32,58 @@ def __init__(self,
                  changeapplier=None,
                  config_wrapper=None,
                  patch_wrapper=None):
+        self.logger = genericUpdaterLogging.get_logger(title="Patch Applier")
         self.config_wrapper = config_wrapper if config_wrapper is not None else ConfigWrapper()
         self.patch_wrapper = patch_wrapper if patch_wrapper is not None else PatchWrapper()
         self.patchsorter = patchsorter if patchsorter is not None else PatchSorter(self.config_wrapper, self.patch_wrapper)
         self.changeapplier = changeapplier if changeapplier is not None else ChangeApplier()
 
     def apply(self, patch):
+        print_to_console=True
+        self.logger.log_notice("Patch application starting.", print_to_console)
+        self.logger.log_notice(f"Patch: {patch}", print_to_console)
+
         # validate patch is only updating tables with yang models
+        self.logger.log_notice("Validating patch is not making changes to tables without YANG models.", print_to_console)
         if not(self.patch_wrapper.validate_config_db_patch_has_yang_models(patch)):
             raise ValueError(f"Given patch is not valid because it has changes to tables without YANG models")
 
         # Get old config
+        self.logger.log_notice("Getting current config db.", print_to_console)
         old_config = self.config_wrapper.get_config_db_as_json()
 
         # Generate target config
+        self.logger.log_notice("Simulating the target full config after applying the patch.", print_to_console)
         target_config = self.patch_wrapper.simulate_patch(patch, old_config)
 
         # Validate target config
+        self.logger.log_notice("Validating target config according to YANG models.", print_to_console)
         if not(self.config_wrapper.validate_config_db_config(target_config)):
             raise ValueError(f"Given patch is not valid because it will result in an invalid config")
 
         # Generate list of changes to apply
+        self.logger.log_notice("Sorting patch updates.", print_to_console)
         changes = self.patchsorter.sort(patch)
+        changes_len = len(changes)
+        self.logger.log_notice(f"The patch was sorted into {changes_len} " \
+                             f"change{'s' if changes_len != 1 else ''}{':' if changes_len > 0 else '.'}",
+                             print_to_console)
+        for change in changes:
+            self.logger.log_notice(f"  * {change}", print_to_console)
 
         # Apply changes in order
+        self.logger.log_notice("Applying changes in order.", print_to_console)
         for change in changes:
             self.changeapplier.apply(change)
 
         # Validate config updated successfully
+        self.logger.log_notice("Verifying patch updates are reflected on ConfigDB.", print_to_console)
         new_config = self.config_wrapper.get_config_db_as_json()
         if not(self.patch_wrapper.verify_same_json(target_config, new_config)):
             raise GenericConfigUpdaterError(f"After applying patch to config, there are still some parts not updated")
 
+        self.logger.log_notice("Patch application completed.", print_to_console)
+
 class ConfigReplacer:
     def __init__(self, patch_applier=None, config_wrapper=None, patch_wrapper=None):
         self.patch_applier = patch_applier if patch_applier is not None else PatchApplier()
@@ -293,11 +313,7 @@ def create_config_rollbacker(self, verbose, dry_run=False):
         return config_rollbacker
 
     def init_verbose_logging(self, verbose):
-        # TODO: implement verbose logging
-        # Usually logs have levels such as: error, warning, info, debug.
-        # By default all log levels should show up to the user, except debug.
-        # By allowing verbose logging, debug msgs will also be shown to the user.
-        pass
+        genericUpdaterLogging.set_verbose(verbose)
 
     def get_config_wrapper(self, dry_run):
         if dry_run:

generic_config_updater/gu_common.py

@@ -6,9 +6,11 @@
 import yang as ly
 import copy
 import re
+from sonic_py_common import logger
 from enum import Enum
 
 YANG_DIR = "/usr/local/yang-models"
+SYSLOG_IDENTIFIER = "GenericConfigUpdater"
 
 class GenericConfigUpdaterError(Exception):
     pass
@@ -691,3 +693,26 @@ def _get_model(self, model, name):
                     return submodel
 
         return None
+
+class TitledLogger(logger.Logger):
+    def __init__(self, syslog_identifier, title, verbose):
+        super().__init__(syslog_identifier)
+        self._title = title
+        if verbose:
+            self.set_min_log_priority_debug()
+
+    def log(self, priority, msg, also_print_to_console=False):
+        combined_msg = f"{self._title}: {msg}"
+        super().log(priority, combined_msg, also_print_to_console)
+
+class GenericUpdaterLogging:
+    def __init__(self):
+        self.set_verbose(False)
+
+    def set_verbose(self, verbose):
+        self._verbose = verbose
+
+    def get_logger(self, title):
+        return TitledLogger(SYSLOG_IDENTIFIER, title, self._verbose)
+
+genericUpdaterLogging = GenericUpdaterLogging()