REPO-1206: "POST /action-executions" returns actionId in response
REPO-1206: "POST /action-executions" returns actionId in response

The response body (previously empty) for a 202 (accepted) now looks
something like this:

```
{
  "entry": {
    "actionId": "string"
  }
}
```

as discussed with Derek during demo.

Alfresco/rest-api-explorer,Alfresco/rest-api-explorer,Alfresco/rest-api-explorer