Add metrics sink to job master

### What changes are proposed in this pull request?

Adding metrics sink to job master.

### Why are the changes needed?

Fix the issue that the job master is unable to sink metrics.

### Does this PR introduce any user facing changes?

Yes, this change will enable users to sink metrics from the job master.

pr-link: #16899
change-id: cid-7394471270d4617007eeb97e1674b90585337624

job/server/src/main/java/alluxio/master/job/JobMaster.java

@@ -184,6 +184,10 @@ public long getNewJobId() {
   @Override
   public void start(Boolean isLeader) throws IOException {
     super.start(isLeader);
+
+    // Start serving metrics system, this will not block
+    MetricsSystem.startSinks(Configuration.getString(PropertyKey.METRICS_CONF_FILE));
+
     // Fail any jobs that were still running when the last job master stopped.
     for (PlanCoordinator planCoordinator : mPlanTracker.coordinators()) {
       if (!planCoordinator.isJobFinished()) {