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-nginx-proxy/tasks/main.yml

@@ -0,0 +1,39 @@
+---
+- ansible.builtin.import_tasks: "{{ role_path }}/tasks/init.yml"
+  tags:
+    - always
+
+# Always validating the configuration, even if `matrix_nginx_proxy: false`.
+# This role performs actions even if the role is disabled, so we need
+# to ensure there's a valid configuration in any case.
+- ansible.builtin.import_tasks: "{{ role_path }}/tasks/validate_config.yml"
+  when: run_setup | bool
+  tags:
+    - setup-all
+    - setup-nginx-proxy
+
+- ansible.builtin.import_tasks: "{{ role_path }}/tasks/ssl/main.yml"
+  when: run_setup | bool
+  tags:
+    - setup-all
+    - setup-nginx-proxy
+    - setup-ssl
+
+- ansible.builtin.import_tasks: "{{ role_path }}/tasks/setup_nginx_proxy.yml"
+  when: run_setup | bool
+  tags:
+    - setup-all
+    - setup-nginx-proxy
+
+- ansible.builtin.import_tasks: "{{ role_path }}/tasks/self_check_well_known.yml"
+  delegate_to: 127.0.0.1
+  become: false
+  when: run_self_check | bool
+  tags:
+    - self-check
+
+- name: Mark matrix-nginx-proxy role as executed
+  ansible.builtin.set_fact:
+    matrix_nginx_proxy_role_executed: true
+  tags:
+    - always