Second iteration of Move Kubernetes from service to Cluster page

What does this MR do?

• Adds a dropdown to choose the forms
• Adds fields in cluster details
• Toggles token visibility
• Creates new forms for GKE and Existing Cluster

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

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [-] Documentation created/updated => This will be followed up in a separated issue
• [-] API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • [-] Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #35616 (closed) Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/39826