Fix custom fields link in sidebar

What does this MR do and why?

Fix custom fields link in sidebar depending on the work item

https://gitlab.slack.com/archives/CD2B8JHGB/p1762378185015359

References

Screenshots or screen recordings

Before	After
	Screen Recording 2025-11-06 at 3.03.46 PM.mov

How to set up and validate locally

1. Go to any group and set some custom fields for epics and issues
2. In this case I created a single select field named SS
3. Create a couple of issues and epics in different projects and root group
4. See that the link of the custom field is correct from wherever it is rendered

MR acceptance checklist

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Related to #579741