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-bigbluebutton/config/main.yml

@@ -32,4 +32,4 @@ docker:
     greenlight:
       enabled:    true
     coturn:
-      enabled:    true
+      internal:   "{{ not 'web-svc-coturn' in group_names | lower }}"