app_confbridge: ConfbridgeList event has standard channel shapshot headers.

* Made the AMI ConfbridgeList action's ConfbridgeList events output all
the standard channel snapshot headers instead of a few hand-coded channel
snapshot headers.  The benefit is that the CallerIDName gets disruptive
characters like CR, LF, Tab, and a few others escaped.  However, an empty
CallerIDName is now output as "<unknown>" instead of "<no name>".

ASTERISK-27651

Change-Id: Iaf7d54a9d40194c2db060bc9b4979fab6720d977