web: enable websockets in config.js
doc: document new ENABLE_WEBSOCKETS variable

prosody: new variables for prosody

prosody: fix check for auth type when including jwt module

Now we get all files from the deb package jitsi-meet-tokens into /prosody-plugins

With /bin/sh one `=` has to be used, otherwise it will always fail with "unexpected operator".

Fixes: https://github.com/jitsi/jitsi-meet/issues/4349

Fixes: https://github.com/jitsi/docker-jitsi-meet/issues/109

It simplifies selecting the desired authentication type, instead of
having a boolean for each.

Store them in the config volume so they are not regenerated on every
boot.

Closes: https://github.com/jitsi/docker-jitsi-meet/issues/71