DataSourceWithBackend: add internal comment for new method (#26139)

(cherry picked from commit 2b6833d0da)

packages/grafana-runtime/src/utils/DataSourceWithBackend.ts

@@ -129,6 +129,11 @@ export class DataSourceWithBackend<
 
   /**
    * Optionally augment the response before returning the results to the
+   *
+   * NOTE: this was added in 7.1 for azure, and will be removed in 7.2
+   * when the entire response pipeline is Observable
+   *
+   * @internal
    */
   processResponse?(res: DataQueryResponse): Promise<DataQueryResponse>;