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-own-webserver.md

@@ -34,7 +34,7 @@ No matter which external webserver you decide to go with, you'll need to:
         matrix_nginx_proxy_enabled: false
         ```
     - if using an external server on another host, add the `<service>_http_host_bind_port` or `<service>_http_bind_port` variables for the services that will be exposed by the external server on the other host. The actual name of the variable is listed in the `roles/<service>/defaults/vars.yml` file for each service. Most variables follow the `<service>_http_host_bind_port` format.
-       
+
       These variables will make Docker expose the ports on all network interfaces instead of localhost only.
       [Keep in mind that there are some security concerns if you simply proxy everything.](https://github.com/matrix-org/synapse/blob/master/docs/reverse_proxy.md#synapse-administration-endpoints)
 
@@ -84,7 +84,7 @@ After following  the [Preparation](#preparation) guide above, you can take a loo
 
 ### Using another external webserver
 
-Feel free to look at the [examples/apache](../examples/apache) directory, or the [template files in the matrix-nginx-proxy role](../roles/matrix-nginx-proxy/templates/nginx/conf.d/).
+Feel free to look at the [examples/apache](../examples/apache) directory, or the [template files in the matrix-nginx-proxy role](../roles/custom/matrix-nginx-proxy/templates/nginx/conf.d/).
 
 
 ## Method 2: Fronting the integrated nginx reverse-proxy webserver with another reverse-proxy