app_broadcast: Add Broadcast application

app_broadcast: Add Broadcast application

Adds a new application, Broadcast, which can be used for
one-to-many transmission and many-to-one reception of
channel audio in Asterisk. This is similar to ChanSpy,
except it is designed for multiple channel targets instead
of a single one. This can make certain kinds of audio
manipulation more efficient and streamlined. New kinds
of audio injection impossible with ChanSpy are also made
possible.

ASTERISK-30180 #close

Change-Id: I7ba72f765dbab9b58deeae028baca3f4f8377726