Resolve "Change new cluster page design to use tabs"

What does this MR do? / Why was this MR needed?

Simplifies Kubernetes configuration by adding both methods of configuring a GKE cluster on the same page.

Are there points in the code the reviewer needs to double check?

Primarily backend consolidation of gcp_controller and user_controller into clusters_controller.

Demo

GIF Demo

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #43446 (closed), #46304 (closed)