Do not define devture_traefik_provider_configuration_extension_yaml in group_vars/matrix_servers

`devture_traefik_provider_configuration_extension_yaml` should not be
set automatically by the playbook. It's a variable to be used by users.

Moreover, setting for for everyone (not just people who have additional JVBs)
means that for most people the following error will be produced:

> 'dict object' has no attribute 'jitsi_jvb_servers'

.. as detailed in https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2844

Fixes a regression introduced in: https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2842

docs/configuring-playbook-jitsi.md

@@ -221,6 +221,42 @@ jitsi_prosody_container_jvb_host_bind_port: 5222
 Applied together this will allow you to provision extra JVB instances which will register themselves with the prosody service and be available for jicofo
 to route conferences too.
 
+To make Traefik reverse-proxy to these additional JVBs (living on other hosts), **you would need to add the following Traefik configuration extension**:
+
+```yaml
+# Traefik proxying for additional JVBs. These can't be configured using Docker
+# labels, like the first JVB is, because they run on different hosts, so we add
+# the necessary configuration to the file provider.
+devture_traefik_provider_configuration_extension_yaml: |
+  http:
+   routers:
+     {% for host in groups['jitsi_jvb_servers'] %}
+
+     additional-{{ hostvars[host]['jitsi_jvb_server_id'] }}-router:
+       entryPoints:
+         - "{{ devture_traefik_entrypoint_primary }}"
+       rule: "Host(`{{ jitsi_hostname }}`) && PathPrefix(`/colibri-ws/{{ hostvars[host]['jitsi_jvb_server_id'] }}/`)"
+       service: additional-{{ hostvars[host]['jitsi_jvb_server_id'] }}-service
+       {% if devture_traefik_entrypoint_primary != 'web' %}
+
+       tls:
+         certResolver: "{{ devture_traefik_certResolver_primary }}"
+
+       {% endif %}
+
+     {% endfor %}
+
+   services:
+     {% for host in groups['jitsi_jvb_servers'] %}
+
+     additional-{{ hostvars[host]['jitsi_jvb_server_id'] }}-service:
+       loadBalancer:
+         servers:
+           - url: "http://{{ host }}:9090/"
+
+     {% endfor %}
+```
+
 ## (Optional) Enable Gravatar
 
 In the default Jisti Meet configuration, gravatar.com is enabled as an avatar service. This results in third party request leaking data to gravatar.

group_vars/matrix_servers

@@ -2555,38 +2555,6 @@ jitsi_self_check_validate_certificates: "{{ false if matrix_ssl_retrieval_method
 # when embedding Jitsi in Matrix rooms.
 jitsi_disable_gravatar: true
 
-# Traefik proxying for additional JVBs. These can't be configured using Docker
-# labels, like the first JVB is, because they run on different hosts, so we add
-# the necessary configuration to the file provider.
-devture_traefik_provider_configuration_extension_yaml: |
-  http:
-   routers:
-     {% for host in groups['jitsi_jvb_servers'] %}
-
-     additional-{{ hostvars[host]['jitsi_jvb_server_id'] }}-router:
-       entryPoints:
-         - "{{ devture_traefik_entrypoint_primary }}"
-       rule: "Host(`{{ jitsi_hostname }}`) && PathPrefix(`/colibri-ws/{{ hostvars[host]['jitsi_jvb_server_id'] }}/`)"
-       service: additional-{{ hostvars[host]['jitsi_jvb_server_id'] }}-service
-       {% if devture_traefik_entrypoint_primary != 'web' %}
-
-       tls:
-         certResolver: "{{ devture_traefik_certResolver_primary }}"
-
-       {% endif %}
-
-     {% endfor %}
-
-   services:
-     {% for host in groups['jitsi_jvb_servers'] %}
-
-     additional-{{ hostvars[host]['jitsi_jvb_server_id'] }}-service:
-       loadBalancer:
-         servers:
-           - url: "http://{{ host }}:9090/"
-
-     {% endfor %}
-
 ######################################################################
 #
 # /jitsi