It is expected to be "focus" in a number of places inside lib-jitsi-meet
and that won't change anytime soon.
Allowing users to change it is just asking for trouble.
Fixes: https://github.com/jitsi/lib-jitsi-meet/issues/2191
Use default values everywhere so they don't need to be specified in the
.env file.
This makes the default .env file much smaller (the larger config options
are documented in the handbook) and should make it easier to port the
setup to runtimes other than Docker Compose.
