improvement: Make broadcast have priority audio while connect to a channel

[silvaalex2021]

hello there!

It would be pretty cool if the "broadcast" dialplan application had an option that allowed it to mute any other audio going to and coming from the PBX while connected to a channel, so the channel could only hear the "broadcaster" without interference.

A use case for such option is when we use broadcast along with a local channel connected to the "playback" application, for example, to play a file for the channel. If the channel is listening to a menu, in hold music, or in a busy confbridge room for example, the mixed sounds can make the caller unable to understand what has been said to them.

So, if we had this option to be set when calling the "broadcast" application, it would help us convey the message more effectively and without the risk of confusion or interference, because all other sounds will be muted (or at least at a much lower volume) for the time the audio is being played!

reference docs: https://docs.asterisk.org/Asterisk_20_Documentation/API_Documentation/Dialplan_Applications/Broadcast/