Add acceptable event log keys to winlog (elastic#21205)

when running filebeat under elasti-agent 'id', 'meta' and 'revision'
are sent as config keys to the winlog input type.  This change allows
those config keys to pass validation.

(cherry picked from commit 499cc94)

winlogbeat/eventlog/factory.go

@@ -28,7 +28,7 @@ import (
 )
 
 var commonConfigKeys = []string{"type", "api", "name", "fields", "fields_under_root",
-	"tags", "processors", "index"}
+	"tags", "processors", "index", "id", "meta", "revision"}
 
 // ConfigCommon is the common configuration data used to instantiate a new
 // EventLog. Each implementation is free to support additional configuration