Fixes: https://github.com/jitsi/docker-jitsi-meet/issues/43

Fixes: https://github.com/jitsi/docker-jitsi-meet/issues/30

The entry is covered by the more generic next one.

Useful if you're running this setup directly on the Internet, with a
Let's Encrypt certificate.

If TLS is terminated elsewhere and then connections are proxied over
HTTP, there is no need for it and it makes initialization a tad slower
on the first run.

Resources:

- https://hynek.me/articles/hardening-your-web-servers-ssl-ciphers/
- https://weakdh.org/sysadmin.html

It's now already there since it's in base.

It's not exposed, we proxy from the web frontend.

Set it directly in the compose file, since it depends on the XMPP
server's hostname.