Refactor TURN/STUN handling:

- Split internal/external Coturn for BBB and Nextcloud
- Added dedicated relay port ranges per app
- Updated env and compose overrides for coturn
- Ensure coturn role is loaded conditionally
- Standardize credential/env passing for coturn
@See https://chatgpt.com/share/68d6f376-4878-800f-b4f7-62822caa49ea

roles/web-app-nextcloud/config/main.yml

@@ -51,6 +51,7 @@ docker:
       version:  "latest"
       backup:
         no_stop_required: false
+      internal: "{{ not 'web-svc-coturn' in group_names | lower }}"
     whiteboard:
       name:     "nextcloud-whiteboard"
       image:    "ghcr.io/nextcloud-releases/whiteboard"