Add developer menu to select max number of connected audio devices

The new developer option modifies the system property
"persist.bluetooth.maxconnectedaudiodevices"; it allows testing
multiple connected devices for A2DP, AVRCP, HFP.

Bug: 71603731
Test: Robolectric test
Change-Id: Ie7887065f98193f4f34e0ff4a29959694e417124