Move roles/matrix* to roles/custom/matrix*

This paves the way for installing other roles into `roles/galaxy` using `ansible-galaxy`,
similar to how it's done in:

- https://github.com/spantaleev/gitea-docker-ansible-deploy
- https://github.com/spantaleev/nextcloud-docker-ansible-deploy

In the near future, we'll be removing a lot of the shared role code from here
and using upstream roles for it. Some of the core `matrix-*` roles have
already been extracted out into other reusable roles:

- https://github.com/devture/com.devture.ansible.role.postgres
- https://github.com/devture/com.devture.ansible.role.systemd_docker_base
- https://github.com/devture/com.devture.ansible.role.timesync
- https://github.com/devture/com.devture.ansible.role.vars_preserver
- https://github.com/devture/com.devture.ansible.role.playbook_runtime_messages
- https://github.com/devture/com.devture.ansible.role.playbook_help

We just need to migrate to those.

roles/custom/matrix-bot-matrix-registration-bot/templates/config/config.yml.j2

@@ -0,0 +1,12 @@
+bot:
+  server: {{ matrix_bot_matrix_registration_bot_bot_server|to_json }}
+  username: {{ matrix_bot_matrix_registration_bot_matrix_user_id_localpart|to_json }}
+  access_token: {{ matrix_bot_matrix_registration_bot_bot_access_token|to_json }}
+api:
+  # API endpoint of the registration tokens
+  base_url: {{ matrix_bot_matrix_registration_bot_api_base_url|to_json }}
+  # Access token of an administrator on the server
+  token: {{ matrix_bot_matrix_registration_bot_api_token|to_json }}
+logging:
+  level: {{ matrix_bot_matrix_registration_bot_logging_level|to_json }}
+