Add new info for auth.log

From 12.1, user information (id and username) are also included on
auth.log. Documentation was updated to reflect this.

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/62756

doc/administration/logs.md

@@ -288,6 +288,9 @@ installations from source.
 It logs information whenever [Rack Attack] registers an abusive request.
+NOTE: **Note:**
+From [%12.1](https://gitlab.com/gitlab-org/gitlab-ce/issues/62756), user id and username are available on this log.
+
 ## `graphql_json.log`
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/issues/59587) in GitLab 12.0.