YARN-11180. Refactor some code of getNewApplication, submitApplication etc. (apache#4618)

Author: slfan1989

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/main/java/org/apache/hadoop/yarn/server/router/RouterAuditLogger.java

@@ -49,6 +49,8 @@ public static class AuditConstants {
     public static final String SUBMIT_NEW_APP = "Submit New App";
     public static final String FORCE_KILL_APP = "Force Kill App";
     public static final String GET_APP_REPORT = "Get Application Report";
+    public static final String TARGET_CLIENT_RM_SERVICE = "RouterClientRMService";
+    public static final String UNKNOWN = "UNKNOWN";
   }
 
   /**