Implement phone.saveDefaultGroupCallJoinAs

[aykutalparslan]

Set the default peer that will be used to join a group call in a specific dialog.

boolFalse#bc799737 = Bool; boolTrue#997275b5 = Bool; ---functions--- phone.saveDefaultGroupCallJoinAs#575e1f8c peer:InputPeer join_as:InputPeer = Bool;