le_audio: Add support for Broadcaster session for Bluetoot stack

Patch extends possibility for stack, Bluetooth Audio Hal part to use
Broadcaster session for broadcasting.

Tag: #feature
Test: atest bluetooth_le_audio_client_test bluetooth_test_broadcaster
Sponsor: jpawlowski@
Bug: 210986334
Change-Id: I4d5402f060a853456751e348072b941173848e04
Merged-In: I4d5402f060a853456751e348072b941173848e04