[le audio] Use gd advertiser for broadcast advertising

Currently broadcast is using the deprecated multi_adv for advertising and this caused conflicts with gd advertiser.
This change updated LEA broadcast to use gd advertiser and change unit tests interface accordingly.

Bug: 268305859
Tag: #refactor
Test: atest bluetooth_test_broadcaster bluetooth_test_broadcaster_state_machine
Change-Id: Ibd67f876d625f23bc3bafa3b71d46c9855781380