Kubernetes agent on GitLab.com feature flag [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

Adds ability to rollout agent-kas per project on GitLab.com. This is in support of #249596 (comment 500042748)

Issue: #276099 (closed)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation ([if required], (https://about.gitlab.com/handbook/engineering/ux/technical-writing/workflow/#when-documentation-is-required)). Already accurate in https://docs.gitlab.com/ee/user/clusters/agent/ version history
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.