YARN-7488. Make ServiceClient.getAppId method public to return ApplicationId for a service name. Contributed by Gour Saha

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-applications/hadoop-yarn-services/hadoop-yarn-services-core/src/main/java/org/apache/hadoop/yarn/service/client/ServiceClient.java

@@ -943,7 +943,7 @@ public class ServiceClient extends AppAdminClient implements SliderExitCodes,
         UserGroupInformation.getCurrentUser(), rpc, address);
   }
 
-  private synchronized ApplicationId getAppId(String serviceName)
+  public synchronized ApplicationId getAppId(String serviceName)
       throws IOException, YarnException {
     if (cachedAppIds.containsKey(serviceName)) {
       return cachedAppIds.get(serviceName);