Add Microsoft.Communication.UserDisconnected Event (Azure#15870)

* Add UserDisconnected Event

* Fix ref and change id to userCommunicationIdentifier

* Add example json

specification/eventgrid/data-plane/Microsoft.Communication/stable/2018-01-01/AzureCommunicationServices.json

@@ -7,6 +7,15 @@
   },
   "paths": {},
   "definitions": {
+    "AcsUserDisconnectedEventData": {
+      "description": "Schema of the Data property of an EventGridEvent for an Microsoft.Communication.UserDisconnected event.",
+      "properties": {
+        "userCommunicationIdentifier": {
+          "description": "The communication identifier of the user who was disconnected",
+          "$ref": "../../../../../communication/data-plane/Common/stable/2021-03-07/common.json#/definitions/CommunicationIdentifierModel"
+        }
+      }
+    },
     "AcsChatMessageReceivedEventData": {
       "description": "Schema of the Data property of an EventGridEvent for a Microsoft.Communication.ChatMessageReceived event.",
       "allOf": [

specification/eventgrid/data-plane/Microsoft.Communication/stable/2018-01-01/examples/user_disconnected.json

@@ -0,0 +1,17 @@
+{
+  "id": "93fa5460-7d6c-4fb7-bbb7-2d56159e98d9",
+  "topic": "/subscriptions/3364013b-4c5c-4dc3-953a-072f091c89a7/resourcegroups/testresources/providers/microsoft.communication/communicationservices/vikramacstestresource",
+  "subject": "user/8:acs:5354158b-17b7-489c-9380-95d8821ff76b_0000000c-6c47-7dfd-6d70-224822000cfb",
+  "data": {
+    "userCommunicationIdentifier": {
+      "rawId": "8:acs:5354158b-17b7-489c-9380-95d8821ff76b_0000000c-6c47-7dfd-6d70-224822000cfb",
+      "communicationUser": {
+        "id": "8:acs:5354158b-17b7-489c-9380-95d8821ff76b_0000000c-6c47-7dfd-6d70-224822000cfb"
+      }
+    }
+  },
+  "eventType": "Microsoft.Communication.UserDisconnected",
+  "dataVersion": "1.0",
+  "metadataVersion": "1",
+  "eventTime": "2021-09-09T21:13:45Z"
+}