Run a Google Ads campaign A/B experiment with the Experiment and ExperimentArm resources

Steps

1. Create the experiment shell with ExperimentService.MutateExperiments: type, suffix, status SETUP, and start_date/end_date, without referencing any campaigns yet.
2. In one MutateExperimentArms call, create exactly one control arm (control=true, referencing the base campaign) and one or more treatment arms, with traffic_split values summing to 100 — this call has no partial-failure support.
3. Query experiment_arm.in_design_campaigns with include_drafts=true to get each treatment arm's auto-created draft campaign, then mutate that draft campaign to apply your test change.
4. Call ExperimentService.ScheduleExperiment, an async long-running operation, to materialize the draft into a live, serving campaign at start_date.
5. Monitor performance via standard reporting, then call EndExperiment (sync) to stop it, PromoteExperiment (async) to apply the treatment to the control, or GraduateExperiment (sync) to spin the treatment off as an independent campaign.