BigBlueButton & Nextcloud:

- Switch to custom BBB Docker repository
- Externalize Coturn and Collabora by default
- Add dedicated 03_dependencies.yml for dependency handling
- Improve env templating with lowercased feature flags
- Add conditional healthcheck for Greenlight
- Refactor TURN/STUN/relay handling with role variable _BBB_COTURN_ROLE
- Extend Collabora/Greenlight dependency wiring in override file
- Nextcloud Talk: refine vars and enable/disable logic with separate plugin/service flags, add network_mode support and conditional nginx proxy block

Ref: https://chatgpt.com/share/68d741ff-a544-800f-9e81-a565e0bab0eb

roles/web-app-bigbluebutton/tasks/03_dependencies.yml

@@ -0,0 +1,17 @@
+- name: "Load Coturn Role for '{{ application_id }}'"
+  include_role:
+    name: web-svc-coturn
+  vars:
+    flush_handlers: true
+  when:    
+    - run_once_web_svc_coturn is not defined
+    - not BBB_COTURN_ENABLED
+
+- name: "Install Collabora Dependency"
+  include_role:
+    name: web-svc-collabora
+  vars:
+    flush_handlers: true
+  when:    
+    - run_once_web_svc_collabora is not defined
+    - not BBB_COLLABORA_ENABLED