Custom monitoring based priority tunnels

This PR implements the Vxlan ECMP priority tunnels where route next hop groups are switched based on the state of the next hop monitor session and their priority.
This implementation allows primary and secondary next-hop groups which are switched based on the monitor state of the next hops.
Please see the included tests to see what this code would do for detail.

Linked-PR: sonic-net/sonic-swss#2671 
Signed-off-by: siqbal1486 <shahzad.iqbal@microsoft.com>

orchagent/orchdaemon.cpp

@@ -55,6 +55,7 @@ BfdOrch *gBfdOrch;
 Srv6Orch *gSrv6Orch;
 FlowCounterRouteOrch *gFlowCounterRouteOrch;
 DebugCounterOrch *gDebugCounterOrch;
+MonitorOrch *gMonitorOrch;
 
 bool gIsNatSupported = false;
 bool gSaiRedisLogRotate = false;
@@ -165,6 +166,8 @@ bool OrchDaemon::init()
     gDirectory.set(vnet_rt_orch);
     VRFOrch *vrf_orch = new VRFOrch(m_applDb, APP_VRF_TABLE_NAME, m_stateDb, STATE_VRF_OBJECT_TABLE_NAME);
     gDirectory.set(vrf_orch);
+    gMonitorOrch = new MonitorOrch(m_stateDb, STATE_VNET_MONITOR_TABLE_NAME); 
+    gDirectory.set(gMonitorOrch);
 
     const vector<string> chassis_frontend_tables = {
         CFG_PASS_THROUGH_ROUTE_TABLE_NAME,
@@ -353,7 +356,7 @@ bool OrchDaemon::init()
      * when iterating ConsumerMap. This is ensured implicitly by the order of keys in ordered map.
      * For cases when Orch has to process tables in specific order, like PortsOrch during warm start, it has to override Orch::doTask()
      */
-    m_orchList = { gSwitchOrch, gCrmOrch, gPortsOrch, gBufferOrch, gFlowCounterRouteOrch, gIntfsOrch, gNeighOrch, gNhgMapOrch, gNhgOrch, gCbfNhgOrch, gRouteOrch, gCoppOrch, gQosOrch, wm_orch, gPolicerOrch, tunnel_decap_orch, sflow_orch, gDebugCounterOrch, gMacsecOrch, gBfdOrch, gSrv6Orch, mux_orch, mux_cb_orch};
+    m_orchList = { gSwitchOrch, gCrmOrch, gPortsOrch, gBufferOrch, gFlowCounterRouteOrch, gIntfsOrch, gNeighOrch, gNhgMapOrch, gNhgOrch, gCbfNhgOrch, gRouteOrch, gCoppOrch, gQosOrch, wm_orch, gPolicerOrch, tunnel_decap_orch, sflow_orch, gDebugCounterOrch, gMacsecOrch, gBfdOrch, gSrv6Orch, mux_orch, mux_cb_orch, gMonitorOrch};
 
     bool initialize_dtel = false;
     if (platform == BFN_PLATFORM_SUBSTRING || platform == VS_PLATFORM_SUBSTRING)