ATLAS-2959: Update metrics query to use index query instead of graph query for faster response

graphdb/api/src/main/java/org/apache/atlas/repository/graphdb/AtlasIndexQuery.java

@@ -44,6 +44,12 @@ public interface AtlasIndexQuery<V, E> {
     Iterator<Result<V, E>> vertices(int offset, int limit);
 
     /**
+     * Gets the total count of query results
+     * @return
+     */
+    Long vertexTotals();
+
+    /**
      * Query result from an index query.
      *
      * @param <V>

graphdb/janus/src/main/java/org/apache/atlas/repository/graphdb/janus/AtlasJanusIndexQuery.java

@@ -77,6 +77,11 @@ public class AtlasJanusIndexQuery implements AtlasIndexQuery<AtlasJanusVertex, A
         return Iterators.transform(results, function);
     }
 
+    @Override
+    public Long vertexTotals() {
+        return query.vertexTotals();
+    }
+
     /**
      * Janus implementation of AtlasIndexQuery.Result.
      */