Move RoundRobin into applicable experiment file

What does this MR do?

It pulls the RoundRobin rollout strategy into the experiment so we don't change the experiment process and opens up this for the ApplicationExperiment.

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because it's limited to a single experiment.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content