feat: add Message Handling for jitsi/lib-jitsi-meet/pull/2339

[Bloodiko]

This is the corresponding xmpp prosody plugin addition in the breakout_rooms plugin for the PR jitsi/lib-jitsi-meet#2339

There may be changes necessary to this, as this lua code is not really complying with the TS Objects types. I was unable to figure out how the objects are correctly typed, so I just gathered as much info as I could from other plugins.
(lua is definitely not my main language, but it was requested in the other PR that this PR should also be created thus, here it is.)

TLDR: Goal is to allow moderators to send single text messages or a whole broadcast text message to all rooms within the same conference.

The "to" argument was chosen to be a composite of source room and occupant/participant nick, to give visual clarity that the message came from a different room.
This can be adjusted if needed.

[jitsi-jenkins]

Hi, thanks for your contribution!
If you haven't already done so, could you please make sure you sign our CLA (https://jitsi.org/icla for individuals and https://jitsi.org/ccla for corporations)? We would unfortunately be unable to merge your patch unless we have that piece :(.

[saghul]

LGTM! @damencho can you PTAL when you get a chance?

[Bloodiko]

Wait a second, the Lua check failed with an unterminated String, I'll check and fix later today.
Didn't knew there is a Lua pipeline.

[github-actions]

This PR has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.