resource_channels.c: add hangup reason "answered_elsewhere".

In ARI, the channels API allows to hangup a channel with a hangup reason.
This commit adds a new reason "answered_elsewhere".
When using a SIP channel, this will eventually allow Asterisk to add a proper
"Reason" header to a CANCEL message.

ASTERISK-26321

Change-Id: Ia97675bd4acd6a7f58eb467953dfb94559f6583d

res/ari/resource_channels.c

@@ -886,6 +886,8 @@ void ast_ari_channels_hangup(struct ast_variable *headers,
 		cause = AST_CAUSE_CONGESTION;
 	} else if (!strcmp(args->reason, "no_answer")) {
 		cause = AST_CAUSE_NOANSWER;
+	} else if(!strcmp(args->reason, "answered_elsewhere")) {
+		cause = AST_CAUSE_ANSWERED_ELSEWHERE;
 	} else {
 		ast_ari_response_error(
 			response, 400, "Invalid Reason",

rest-api/api-docs/channels.json

@@ -400,7 +400,8 @@
 									"normal",
 									"busy",
 									"congestion",
-									"no_answer"
+									"no_answer",
+									"answered_elsewhere"
 								]
 							}
 						}