Add back string op type to IndexRequest

This was removed by accident I think, and it breaks backward comp. on the Java API in minor 1.3 version
closes #7387

src/main/java/org/elasticsearch/action/index/IndexRequest.java

@@ -483,6 +483,15 @@ public class IndexRequest extends ShardReplicationOperationRequest<IndexRequest>
         return this;
     }
 
+    /**
+     * Sets a string representation of the {@link #opType(org.elasticsearch.action.index.IndexRequest.OpType)}. Can
+     * be either "index" or "create".
+     */
+    public IndexRequest opType(String opType) throws ElasticsearchIllegalArgumentException {
+        return opType(OpType.fromString(opType));
+    }
+
+
     /**
      * Set to <tt>true</tt> to force this index to use {@link OpType#CREATE}.
      */