Initial work on matrix-homeserver-proxy role and eliminating matrix-nginx-proxy

This is still very far from usable.

Various bridges and bots are still talking to
`matrix-nginx-proxy` instead of the new `matrix-homeserver-proxy` role.
These services need to be reworked. While reworking them,
various cleanups are being done as well as adding Traefik-labels to
those that need them.

roles/custom/matrix-bot-chatgpt/tasks/validate_config.yml

@@ -8,6 +8,8 @@
   with_items:
     - {'name': 'matrix_bot_chatgpt_openai_api_key', when: true}
     - {'name': 'matrix_bot_chatgpt_matrix_bot_username', when: true}
+    - {'name': 'matrix_bot_chatgpt_container_network', when: true}
+    - {'name': 'matrix_bot_chatgpt_matrix_homeserver_url', when: true}
 
 - name: Fail if OpenAI configuration not up-to-date.
   ansible.builtin.fail: