Retrieves a label with a given name, or creates one if it doesn't exist.
Successful calls to this endpoint always return a label, which can be passed to subsequent requests.
For example, in the Contacts API, Label Contact and Unlabel Contact requests will fail if you include a nonexistant label. To ensure successful calls, you can call this endpoint first, and then use the response in the label and unlabel requests.
To find an existing label without potentially creating a new one, use Get Label or List Labels.
You can only call this method when authenticated as a Wix app or Wix user identity.