Initial work on Traefik support

This gets us started on adding a Traefik role and hooking Traefik:

- directly to services which support Traefik - we only have a few of
  these right now, but the list will grow

- to matrix-nginx-proxy for most services that integrate with
  matrix-nginx-proxy right now

Traefik usage should be disabled by default for now and nothing should
change for people just yet.

Enabling these experiments requires additional configuration like this:

```yaml
devture_traefik_ssl_email_address: '.....'

matrix_playbook_traefik_role_enabled: true
matrix_playbook_traefik_labels_enabled: true

matrix_ssl_retrieval_method: none

matrix_nginx_proxy_https_enabled: false

matrix_nginx_proxy_container_http_host_bind_port: ''
matrix_nginx_proxy_container_federation_host_bind_port: ''

matrix_nginx_proxy_trust_forwarded_proto: true

matrix_nginx_proxy_x_forwarded_for: '$proxy_add_x_forwarded_for'

matrix_coturn_enabled: false
```

What currently works is:
reverse-proxying for all nginx-proxy based services **except** for the Matrix homeserver
(both Client-Server an Federation traffic for the homeserver don't work yet)

roles/custom/matrix-nginx-proxy/templates/systemd/matrix-nginx-proxy.service.j2

@@ -24,6 +24,7 @@ ExecStartPre={{ devture_systemd_docker_base_host_command_docker }} create \
 			--cap-drop=ALL \
 			--read-only \
 			--tmpfs=/tmp:rw,noexec,nosuid,size={{ matrix_nginx_proxy_tmp_directory_size_mb }}m \
+			--label-file={{ matrix_nginx_proxy_base_path }}/labels \
 			--network={{ matrix_nginx_proxy_container_network }} \
 			{% if matrix_nginx_proxy_container_http_host_bind_port %}
 			-p {{ matrix_nginx_proxy_container_http_host_bind_port }}:8080 \