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.

docs/configuring-playbook-jitsi.md

@@ -14,7 +14,7 @@ Before installing Jitsi, make sure you've created the `jitsi.DOMAIN` DNS record.
 You may also need to open the following ports to your server:
 
 - `4443/tcp` - RTP media fallback over TCP
-- `10000/udp` - RTP media over UDP. Depending on your firewall/NAT setup, incoming RTP packets on port `10000` may have the external IP of your firewall as destination address, due to the usage of STUN in JVB (see [`matrix_jitsi_jvb_stun_servers`](../roles/matrix-jitsi/defaults/main.yml)).
+- `10000/udp` - RTP media over UDP. Depending on your firewall/NAT setup, incoming RTP packets on port `10000` may have the external IP of your firewall as destination address, due to the usage of STUN in JVB (see [`matrix_jitsi_jvb_stun_servers`](../roles/custom/matrix-jitsi/defaults/main.yml)).
 
 
 ## Installation