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-synapse/tasks/self_check_client_api.yml

@@ -0,0 +1,21 @@
+---
+
+- name: Check Matrix Client API
+  ansible.builtin.uri:
+    url: "{{ matrix_synapse_client_api_url_endpoint_public }}"
+    follow_redirects: none
+    validate_certs: "{{ matrix_synapse_self_check_validate_certificates }}"
+  register: result_matrix_synapse_client_api
+  ignore_errors: true
+  check_mode: false
+  when: matrix_synapse_enabled | bool
+
+- name: Fail if Matrix Client API not working
+  ansible.builtin.fail:
+    msg: "Failed checking Matrix Client API is up at `{{ matrix_server_fqn_matrix }}` (checked endpoint: `{{ matrix_synapse_client_api_url_endpoint_public }}`). Is Synapse running? Is port 443 open in your firewall? Full error: {{ result_matrix_synapse_client_api }}"
+  when: "matrix_synapse_enabled | bool and (result_matrix_synapse_client_api.failed or 'json' not in result_matrix_synapse_client_api)"
+
+- name: Report working Matrix Client API
+  ansible.builtin.debug:
+    msg: "The Matrix Client API at `{{ matrix_server_fqn_matrix }}` (checked endpoint: `{{ matrix_synapse_client_api_url_endpoint_public }}`) is working"
+  when: matrix_synapse_enabled | bool