✨ Add mod_turncredentials to prosody

[madmath03]

✨ Add mod_turncredentials to prosody

There have been so many TURN Pull Requests (latest active being #163) and none being validated yet that I'm thinking it might be good to do it step by step.

• ✨ Env var to setup STUN/TURN #835 Provides env var to configure Jitsi Web STUN support
• this one just adds mod_turncredentials.lua to prosody. Without any other developments, TURN can be setup simply with GLOBAL_* env var:

GLOBAL_MODULES=turncredentials
GLOBAL_CONFIG=turncredentials_secret = "mysupersecuresharedturnsecret";\nturncredentials_host = "turn.example.com";\nturncredentials_port = 5349;

@saghul what do you think ?

[goacid]

This is already in the PR for adding Turn
#667

[saghul]

#667 is indeed the way to go here.