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-synapse/templates/synapse/ext/s3-storage-provider/database.yaml.j2

@@ -0,0 +1,5 @@
+user: {{ matrix_synapse_database_user | to_json }}
+password: {{ matrix_synapse_database_password | to_json }}
+database: {{ matrix_synapse_database_database | to_json }}
+host: {{ matrix_synapse_database_host | to_json }}
+port: {{ matrix_synapse_database_port | to_json }}