feat: ARI "ChannelToneDetected" event

A stasis event is now produced when using the TONE_DETECT dialplan
function. This event is published over ARI using the ChannelToneDetected
event. This change does not make it available over AMI.

Fixes: #811

UserNote: Setting the TONE_DETECT dialplan function on a channel
in ARI will now cause a ChannelToneDetected ARI event to be raised
when the specified tone is detected.

rest-api/api-docs/events.json

@@ -178,6 +178,7 @@
 				"ChannelUserevent",
 				"ChannelHangupRequest",
 				"ChannelVarset",
+				"ChannelToneDetected",
 				"ChannelTalkingStarted",
 				"ChannelTalkingFinished",
 				"ChannelHold",
@@ -759,6 +760,17 @@
 				}
 			}
 		},
+		"ChannelToneDetected": {
+			"id": "ChannelToneDetected",
+			"description": "Tone was detected on the channel.",
+			"properties": {
+				"channel": {
+					"required": true,
+					"type": "Channel",
+					"description": "The channel the tone was detected on."
+				}
+			}
+		},
 		"ChannelTalkingStarted": {
 			"id": "ChannelTalkingStarted",
 			"description": "Talking was detected on the channel.",