Detect taskId changes in frontend and send the metadata along with xml payload

[mirkoSekulic]

There is no good solution to detect changes only based on new xml, so we need to send metadata that includes taskId changes in order to fire correct events in backend.

Metadata that we're sending along with content xml:

{
  "taskIdChanges": [
     {
        "oldId": "Task_1",
        "newId": "newId"   
     }
  ]
}

An example of the request to the new endpoint can be found here.

[nkylstad]

Should be solved by #12272