apps/app_mixmonitor: Add Options To Play Beep At Start Or Stop

We have a new periodic beep feature but sometimes a user needs some sort of
feedback, without the need to have a periodic beep during the recording, to let
them know that MixMonitor started recording or ended the recording.  The use
case where this patch is being used is when using Dynamic Features to start and
end MixMonitor.

This patch adds an option to play a beep when MixMonitor starts and an option to
play a beep when MixMonitor ends.

ASTERISK-24051 #close
Reported by: Michael L. Young
patches:
  mixmonitor-play-beep-start-stop.diff
                                     uploaded by Michael L. Young (license 5026)

Review: https://reviewboard.asterisk.org/r/3820/


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@419238 f38db490-d61c-443f-a65b-d21fe96a405b