Promotes the trial campaign thus applying changes in the trial campaign to the base campaign. This method returns a long running operation that tracks the promotion of the experiment campaign. If it fails, a list of errors can be retrieved using the ListExperimentAsyncErrors method. The operation's metadata will be a string containing the resource name of the created experiment. List of thrown errors: AuthenticationError AuthorizationError ExperimentError HeaderError InternalError QuotaError RequestError