app_queue: Add QueueWithdrawCaller AMI action

This adds a new AMI action called QueueWithdrawCaller.
This AMI action makes it possible to withdraw a caller from a queue,
in a safe and a generic manner.
This can be useful for retrieving a specific call and
dispatching it to a specific extension.
It works by signaling the caller to exit the queue application
whenever it can. Therefore, it is not guaranteed
that the call will leave the queue.

ASTERISK-29909 #close

Change-Id: Ic15aa238e23b2884abdcaadff2fda7679e29b7ec