Support short reference to epics from project entities

What does this MR do?

When an epic is referenced from a project as a short reference (&ID eg. &7) it is extracted as an epic with iid 7 from direct parent of the project.

• group is added to the Banzai context even when called from project entities - group that the project belongs to is used (direct parent)

An epic from a group that is a direct parent of a project entity the epic is referenced from is rendered as short reference &ID

• if to_reference is called from the project that is a direct descendant of the epic group short reference is used

What are the relevant issue numbers?

Closes #7287 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?