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-nextcloud/templates/nginx/docker.conf.j2

@@ -190,6 +190,7 @@ http {
             proxy_read_timeout 3600;
         }
 
+{% if NEXTCLOUD_TALK_SERVICE_ENABLED %}
         location {{ NEXTCLOUD_TALK_LOCATION }} {
             proxy_pass         http://talk:{{ NEXTCLOUD_TALK_PORT_INTERNAL }}/;
             proxy_http_version 1.1;
@@ -198,5 +199,7 @@ http {
             proxy_set_header   Connection        "upgrade";
             proxy_read_timeout 3600;
         }
+{% endif %}
+
     }
 }