chore: add docker compose for auth provider

Add ldap tes server to allow to easily work with that

Signed-off-by: Philip Molares <philip.molares@udo.edu>

backend/docker-compose.auth.yml

@@ -0,0 +1,10 @@
+# SPDX-FileCopyrightText: 2026 The HedgeDoc developers (see AUTHORS file)
+# SPDX-License-Identifier: AGPL-3.0-only
+---
+services:
+  ldap:
+    # renovate: datasource=docker depName=rroemhild/test-openldap
+    image: rroemhild/test-openldap
+    ports:
+      - "10389:10389"
+      - "10636:10636"