Mark syslog processor as GA and improve documentation (#36417)

- Removed the experimental tag for the syslog processor
- Improve documentation of the syslog processor to note that it does
not directly handle receiving external messages.

CHANGELOG.next.asciidoc

@@ -150,6 +150,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 - Add warning message to SysV init scripts for RPM-based systems that lack `/etc/rc.d/init.d/functions`. {issue}35708[35708] {pull}36188[36188]
 - Mark `translate_sid` processor is GA. {issue}36279[36279] {pull}36280[36280]
 - dns processor: Add support for forward lookups (`A`, `AAAA`, and `TXT`). {issue}11416[11416] {pull}36394[36394]
+- Mark `syslog` processor as GA, improve docs about how processor handles syslog messages. {issue}36416[36416] {pull}36417[36417]
 
 *Auditbeat*
 

libbeat/processors/syslog/docs/syslog.asciidoc

@@ -5,7 +5,12 @@
 <titleabbrev>syslog</titleabbrev>
 ++++
 
-experimental[]
+The syslog processor parses RFC 3146 and/or RFC 5424 formatted syslog messages
+that are stored in a field. The processor itself does not handle receiving syslog
+messages from external sources. This is done through an input, such as the TCP
+input. Certain integrations, when enabled through configuration, will embed the
+syslog processor to process syslog messages, such as Custom TCP Logs and
+Custom UDP Logs.
 
 [float]
 ==== Configuration