Resolve ""new look" causes attach-file to ignore external_url"

What does this MR do and why?

This MR changes the calculation of the uploadsPath to use parent namespace web url as a base.

References

Related issue: Related to #535633 (closed)

Screenshots or screen recordings

No visual changes

How to set up and validate locally

1. Open an epic and try uploading images to description, new comment, new reply in the thread, edited comment.
2. Create a child issue and open it in the drawer.
3. Repeat the uploading test

MR acceptance checklist

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

Related to #535633 (closed)