Show reference link for epics linked

What does this MR do and why?

Show reference path for epic work item linked via # key.

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

Before	After

How to set up and validate locally

To test this locally, you need to enable WI at group level, so you will have to enable these feature flags namespace_level_work_items (If you are still unable to access work-item page for an epic then enable/disable FF from this list - &11777 )

1. Visit Epics page and try to create a new EPICs(If all relevant FF's are enabled then you should see a modal when you click on New Epic)
2. Create a sub-group and create a new epic in it as well
3. Open the newly created epic in parent group and replace epics in the URL with work_items, SO the target URL would be something like http://127.0.0.1:3000/groups/flightjs/-/work_items/6
4. In the comment section upon, on entering # you should be able to see the epic work item from sub-group and upon selecting it and clicking preview you should be able to see the reference value with full path and the link pointing to the epic work item.