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-aux/tasks/main.yml

@@ -0,0 +1,7 @@
+---
+
+- ansible.builtin.import_tasks: "{{ role_path }}/tasks/setup.yml"
+  when: run_stop | bool
+  tags:
+    - setup-all
+    - setup-aux-files

roles/custom/matrix-aux/tasks/setup.yml

@@ -0,0 +1,20 @@
+---
+
+- name: Ensure AUX directories are created
+  ansible.builtin.file:
+    dest: "{{ item.dest }}"
+    state: directory
+    owner: "{{ item.owner | default(matrix_user_username) }}"
+    group: "{{ item.group | default(matrix_user_groupname) }}"
+    mode: "{{ item.mode | default(matrix_aux_directory_default_mode) }}"
+  with_items: "{{ matrix_aux_directory_definitions }}"
+
+- name: Ensure AUX files are created
+  ansible.builtin.copy:
+    src: "{{ item.src if 'src' in item else omit }}"
+    content: "{{ item.content if 'content' in item else omit }}"
+    dest: "{{ item.dest }}"
+    owner: "{{ item.owner | default(matrix_user_username) }}"
+    group: "{{ item.group | default(matrix_user_groupname) }}"
+    mode: "{{ item.mode | default(matrix_aux_file_default_mode) }}"
+  with_items: "{{ matrix_aux_file_definitions }}"