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/setup_matrix_user.yml

@@ -0,0 +1,27 @@
+---
+
+- name: Ensure Matrix group is created
+  ansible.builtin.group:
+    name: "{{ matrix_user_groupname }}"
+    gid: "{{ omit if matrix_user_gid is none else matrix_user_gid }}"
+    state: present
+  register: matrix_group
+
+- name: Set Matrix Group GID Variable
+  ansible.builtin.set_fact:
+    matrix_user_gid: "{{ matrix_group.gid }}"
+
+- name: Ensure Matrix user is created
+  ansible.builtin.user:
+    name: "{{ matrix_user_username }}"
+    uid: "{{ omit if matrix_user_uid is none else matrix_user_uid }}"
+    state: present
+    group: "{{ matrix_user_groupname }}"
+    home: "{{ matrix_base_data_path }}"
+    create_home: false
+    system: true
+  register: matrix_user
+
+- name: Set Matrix Group UID Variable
+  ansible.builtin.set_fact:
+    matrix_user_uid: "{{ matrix_user.uid }}"