Pre-fill find file search with the current directory

What does this MR do and why?

Automatically inserts the current directory into the find file modal to allow for quicker search.

#22426 (closed)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

How to set up and validate locally

• Open a folder in a repository (http://gdk.test:3000/gitlab-org/gitlab-test/-/tree/master/files)
• Trigger the find file modal (t on keyboard)
• Current directory (files) should be in the modal