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-client-element/tasks/self_check.yml

@@ -0,0 +1,22 @@
+---
+
+- ansible.builtin.set_fact:
+    matrix_client_element_url_endpoint_public: "https://{{ matrix_server_fqn_element }}/config.json"
+
+- name: Check Element
+  ansible.builtin.uri:
+    url: "{{ matrix_client_element_url_endpoint_public }}"
+    follow_redirects: none
+    validate_certs: "{{ matrix_client_element_self_check_validate_certificates }}"
+  register: matrix_client_element_self_check_result
+  check_mode: false
+  ignore_errors: true
+
+- name: Fail if Element not working
+  ansible.builtin.fail:
+    msg: "Failed checking Element is up at `{{ matrix_server_fqn_element }}` (checked endpoint: `{{ matrix_client_element_url_endpoint_public }}`). Is Element running? Is port 443 open in your firewall? Full error: {{ matrix_client_element_self_check_result }}"
+  when: "matrix_client_element_self_check_result.failed or 'json' not in matrix_client_element_self_check_result"
+
+- name: Report working Element
+  ansible.builtin.debug:
+    msg: "Element at `{{ matrix_server_fqn_element }}` is working (checked endpoint: `{{ matrix_client_element_url_endpoint_public }}`)"