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-conduit/vars/main.yml

@@ -0,0 +1,6 @@
+---
+matrix_conduit_client_api_url_endpoint_public: "https://{{ matrix_server_fqn_matrix }}/_matrix/client/versions"
+matrix_conduit_federation_api_url_endpoint_public: "https://{{ matrix_server_fqn_matrix }}:{{ matrix_federation_public_port }}/_matrix/federation/v1/version"
+
+# Tells whether this role had executed or not. Toggled to `true` during runtime.
+matrix_conduit_role_executed: false