Allow options to be passed to rollout

This also removes the First rollout strategy and just implements this very basic rollout concept in the base.

This isn't used yet (so there's no added tests to cover it exactly,) but the plan is to pick it back up for https://gitlab.com/gitlab-org/gitlab-experiment/-/merge_requests/89 -- where it would be nice to at least hardcode these options, and eventually we can improve it by pulling this in from something that can be changed via an interface or chatops command.