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-postgres/templates/usr-local-bin/matrix-postgres-cli.j2

@@ -0,0 +1,13 @@
+#jinja2: lstrip_blocks: "True"
+#!/bin/bash
+
+docker run \
+	-it \
+	--rm \
+	--user={{ matrix_user_uid }}:{{ matrix_user_gid }} \
+	--cap-drop=ALL \
+	--env-file={{ matrix_postgres_base_path }}/env-postgres-psql \
+	--network {{ matrix_docker_network }} \
+	{{ matrix_postgres_docker_image_to_use }} \
+	psql -h {{ matrix_postgres_connection_hostname }} \
+	"$@"