app_queue: Log reason for PAUSEALL/UNPAUSEALL

We needed the reason for our reporting when agents pause/unpause all of
their queues at once.  This is a small, simple patch that adds a reason
for PAUSEALL and UNPAUSEALL.  I have been using it in production for years.

ASTERISK-26920 #close

Change-Id: Ifb3f0d1a0abd5194253d9794023546e1395baf3d