Launch standalone domain purchase a/b test

[anneforbush]

This task pertains simply to setting the test live -- not the development work needed to prepare the experiment.

[github-actions]

This issue is stale because it has been 180 days with no activity. You can keep the issue open by adding a comment. If you do, please provide additional context and explain why you’d like it to remain open. You can also close the issue yourself — if you do, please add a brief explanation and apply one of relevant issue close labels.