EventService: Add event log support with inotify

Add event logs support
 - Event log monitor by adding inotify on redfish log file.
 - Read event logs from "/var/log/redfish" file.
 - Filter the event logs using configured settings.
 - Format the event log data as per Events schema.
 - Send event log information to subcribed client.

Tested:
 - Added new event log subscription with filters
   and verified the event logs on event listener.
 - Ran redfish validater successfully.
 - Disabled BMCWEB_ENABLE_REDFISH_DBUS_LOG_ENTRIES
   and build successful.

   Event on listener looks as below:
{
   "@odata.type":"#Event.v1_4_0.Event",
   "Events":[
      {
         "Context":"CustomText",
         "EventId":"94787",
         "EventTimestamp":"1970-01-02T02:19:47+00:00",
         "EventType":"Event",
         "Message":"Memory ThermTrip asserted: .",
         "MessageArgs":[
            ""
         ],
         "MessageId":"OpenBMC.0.1.MemoryThermTrip",
         "Severity":"Critical"
      }
   ],
   "Id":"3",
   "Name":"Event Log"
}

Change-Id: Ie87322ff59f9f7caa26fb18d2e3b8d7af77ec540
Signed-off-by: AppaRao Puli <apparao.puli@linux.intel.com>
diff --git a/src/webserver_main.cpp b/src/webserver_main.cpp
index 4bdf880..2763991 100644
--- a/src/webserver_main.cpp
+++ b/src/webserver_main.cpp
@@ -115,6 +115,15 @@
 
     redfish::RedfishService redfish(app);
 
+#ifndef BMCWEB_ENABLE_REDFISH_DBUS_LOG_ENTRIES
+    int rc = redfish::EventServiceManager::startEventLogMonitor(*io);
+    if (rc)
+    {
+        BMCWEB_LOG_ERROR << "Redfish event handler setup failed...";
+        return rc;
+    }
+#endif
+
     app.run();
     io->run();