Add ambiguous ref modal

What does this MR do and why?

Adds a modal to help guide the user when an ambiguous ref is selected.

Screenshots or screen recordings

Page	Modal	Redirected
Repository
Tree
Blob

How to set up and validate locally

Note, this MR excludes the backend work that is needed to display the modal.

1. Apply the backend changes on which this MR depends:
   • curl https://gitlab.com/gitlab-org/gitlab/-/merge_requests/133093.diff | git apply
2. Open a project that has a tag and branch with the same name.
   • Alternatively, clone my test project which has a colliding ref called test.
3. View the Repository, Tree, or Blob with the colliding ref selected from the ref dropdown.
4. The Ambiguous ref popup should be displayed.
5. The View tag/branch button should redirect the user to the preferred ref.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #408388 (closed)