Create a Preflight Endpoint for ARO HCP

[mbarnes]

What this PR does

Before this PR:

No preflight endpoint. ☹️

After this PR:

Preflight endpoint! 😄

Jira: ARO-6156 : Create a Preflight Endpoint for ARO HCP
Link to demo recording:

Special notes for your reviewer

RP contract documentation: What is Preflight?

Per acceptance criteria, this just performs static validation and does not call out to Cluster Service.

Checklist

This checklist is not enforcing, but it's a reminder of items that could be relevant to every PR.
Approvers are expected to review this list.

• PR: The PR description is expressive enough and will help future contributors
• Code: Write code that humans can understand and Keep it simple
• Refactor: You have left the code cleaner than you found it (Boy Scout Rule)
• Upgrade: Impact of this change on upgrade flows was considered and addressed if required
• Deployment: The deployment process was considered and addressed if required
• Testing: New code requires new unit tests.
• Documentation: Is the documentation updated? Either in the doc located in focus area, in the README or in the code itself.
• Customers: Is this change affecting customers? Is the release plan considered?

[mjlshen]

Thanks for the links to ARM preflight documentation as well!