Add DORA DF note in VSA docs

This change adds a note to the VSA docs. DORA based deployment frequency
is now available for premium customers.

doc/user/group/value_stream_analytics/index.md

@@ -99,6 +99,8 @@ The "Recent Activity" metrics near the top of the page are measured as follows:
 1. To see deployment metrics, you must have a
    [production environment configured](../../../ci/environments/index.md#deployment-tier-of-environments).
+> Since GitLab 14.3, DORA API-based deployment metrics are [available](https://gitlab.com/gitlab-org/gitlab/-/issues/337256) in group-level Value Stream Analytics for Premium customers as well.
+
 You can learn more about these metrics in our [analytics definitions](../../analytics/index.md).
 ![Value stream analytics time metrics](img/vsa_time_metrics_v13_12.png "Time metrics for value stream analytics")