ARI/AMI: Include language in standard channel snapshot output

The channel "language" was already part of a channel snapshot, however is was
not sent out over AMI or ARI. This patch makes it so the channel "language" is
included in the appropriate AMI or ARI events.

ASTERISK-24553 #close
Reported by: Matt Jordan
Review: https://reviewboard.asterisk.org/r/4245/
........

Merged revisions 429204 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/13@429206 65c4cc65-6c06-0410-ace0-fbb531ad65f3

rest-api/api-docs/channels.json

@@ -1465,6 +1465,11 @@
 					"required": true,
 					"type": "Date",
 					"description": "Timestamp when channel was created"
+				},
+				"language": {
+					"required": true,
+					"type": "string",
+					"description": "The default spoken language"
 				}
 			}
 		}