docker-compose.yml - reverse proxy the jellyfin container as virtual host

we need to take it of host network mode, add it to the proxy-tier and
default networks, then enable proxying and lets-encrypt.

Tested, works.

snackpot.yml

@@ -8,6 +8,7 @@
     nextcloud_hostname: nc.noodlefactory.co.uk
     nextcloud_db_user: nextcloud
     nextcloud_db: nextcloud
+    jellyfin_hostname: jf.noodlefactory.co.uk
     letsencrypt_email: webmaster@noodlefactory.co.uk
     docker_compose_base_dir: /opt/docker-compose
     firewall_ports: