Create a new holdout in the specified project.
The project key
The environment key
A human-friendly name for the holdout
A key that identifies the holdout
Description of the holdout
The chosen randomization unit for the holdout base experiment
The attributes that the holdout iteration’s results can be sliced by
Audience allocation for the holdout
The key of the primary metric for this holdout
Details on the metrics for this experiment
The key of the flag that the holdout is dependent on
Maintainer id
Holdout response
The percentage of traffic allocated to this holdout.