Add bulk_import details page behind a feature flag

What does this MR do and why?

This is behind the feature flag bulk_import_details_page. Add an empty page (mostly reusing the code + components from import_details_app.vue) which will be used to show all failures that occur with a bulk_import entity.

Screenshots or screen recordings

How to set up and validate locally

Go to http://127.0.0.1:3000/import/bulk_imports/details.

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 #386138 (closed)