app_originate: Add option to execute gosub prior to dial

Issue/patch ASTERISK-26587 was inspired by issue ASTERISK-22992
that requested ability to add callerid into app_originate.
Comments in that issue suggested that it was better solved by
adding an option to gosub prior to originating the call.  The
attached patch implements this much like app_dial with two
options one to gosub on the originating channel and one to gosub
on the newly created channel and behaves just like app_dial.
I have tested this patch by adding callerid info to the new
channel and also SIPAddHeader (to e.g. add header to force auto
answer) and confirmed it works.  Have also tested both 'exten'
and 'app' versions of app_originate.

Opened by: dkerr
Patch by: dkerr

Change-Id: I36abc39b58567ffcab4a636ea196ef48be234c57