message & stasis/messaging: make text message variables work in ARI

When a text message was received any associated variable was not written to
the ARI TextMessageReceived event. This occurred because Asterisk only wrote
out "send" variables. However, even those "send" variables would fail ARI
validation due to a TextMessageVariable formatting bug.

Since it seems the TextMessageReceived event has never been able to include
actual variables it was decided to remove the TextMessageVariable object type
from ARI, and simply return a JSON object of key/value pairs for variables.
This aligns more with how the ARI sendMessage handles variables, and other
places in ARI.

That being the case, and since this is technically an API breaking change (no
one should really be affected since things never really worked) the ARI version
was updated to reflect that.

ASTERISK-28755 #close

Change-Id: Ia6051c01a53b30cf7edef84c27df4ed4479b8b6f

rest-api/api-docs/endpoints.json

@@ -233,22 +233,6 @@
 				}
 			}
 		},
-		"TextMessageVariable": {
-			"id": "TextMessageVariable",
-			"description": "A key/value pair variable in a text message.",
-			"properties": {
-				"key": {
-					"type": "string",
-					"description": "A unique key identifying the variable.",
-					"required": true
-				},
-				"value": {
-					"type": "string",
-					"description": "The value of the variable.",
-					"required": true
-				}
-			}
-		},
 		"TextMessage": {
 			"id": "TextMessage",
 			"description": "A text message.",
@@ -269,8 +253,8 @@
 					"required": true
 				},
 				"variables": {
-					"type": "List[TextMessageVariable]",
-					"description": "Technology specific key/value pairs associated with the message.",
+					"type": "object",
+					"description": "Technology specific key/value pairs (JSON object) associated with the message.",
 					"required": false
 				}
 			}