Include channel uniqueid in "AsyncAGI" and "AGIExec" events.

* Added AMI event documentation for AsyncAGI and AGIExec events.

(closes issue ASTERISK-20318)
Reported by: Dan Cropp
Patches:
      res_agi_patch.txt (license #6422) patch uploaded by Dan Cropp
      modified for trunk.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@374075 65c4cc65-6c06-0410-ace0-fbb531ad65f3