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-base/tasks/server_base/setup_debian.yml

@@ -0,0 +1,41 @@
+---
+
+- name: Ensure APT usage dependencies are installed
+  ansible.builtin.apt:
+    name:
+      - apt-transport-https
+      - ca-certificates
+      - gnupg
+    state: present
+    update_cache: true
+
+- name: Ensure Docker's APT key is trusted
+  ansible.builtin.apt_key:
+    url: "https://download.docker.com/linux/{{ ansible_distribution | lower }}/gpg"
+    id: 9DC858229FC7DD38854AE2D88D81803C0EBFCD88
+    state: present
+  register: add_repository_key
+  ignore_errors: true
+  when: matrix_docker_installation_enabled | bool and matrix_docker_package_name == 'docker-ce'
+
+- name: Ensure Docker repository is enabled
+  ansible.builtin.apt_repository:
+    repo: "deb [arch={{ matrix_debian_arch }}] https://download.docker.com/linux/{{ ansible_distribution | lower }} {{ ansible_distribution_release }} stable"
+    state: present
+    update_cache: true
+  when: matrix_docker_installation_enabled | bool and matrix_docker_package_name == 'docker-ce'
+
+- name: Ensure APT packages are installed
+  ansible.builtin.apt:
+    name:
+      - "{{ matrix_ntpd_package }}"
+    state: present
+    update_cache: true
+
+- name: Ensure Docker is installed
+  ansible.builtin.apt:
+    name:
+      - "{{ matrix_docker_package_name }}"
+      - "python{{ '3' if ansible_python.version.major == 3 else '' }}-docker"
+    state: present
+  when: matrix_docker_installation_enabled | bool