Use projectRootPath to compose breadcrumb links

What does this MR do and why?

Use projectRootPath to compose breadcrumb links

For instances with a relative url, the root path is need to compose a correct breadcrumb link.

Changelog: fixed

References

• Breadcrumb links in tree views are incorrect for installations configured with relative URLs

Screenshots or screen recordings

Context	Before	After
instance without relative url

How to set up and validate locally

1. Configure your GDK to use a relative url. You want relative_url_root value to be set to for example /gitlab
2. Run gdk reconfigure
3. Go to Project / Repository. Remember to edit your remembered URL to include /gitlab, so for example: http://gdk.test:8080/gitlab/flightjs/Flight
4. Verify that breadcrumbs of the repository include /gitlab

Disclaimer: I wasn't able to reconfigure my GDK correctly. The page was loading with a lot of errors and it did not render correctly. I was able to verify with Vue dev tools, that a correct string is passed to the breadcrumbs component though:

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Related to #550053 (closed)