Add system notes for issue - epic association
What does this MR do?
It adds system notes for
- adding an issue to an epic
- removing an issue from an epic
System notes are created for both issue and epic.
The same action (=icon) as for related issues is used.
Are there points in the code the reviewer needs to double check?
Why was this MR needed?
Screenshots (if relevant)
Does this MR meet the acceptance criteria?
- Changelog entry added, if necessary
- Documentation created/updated
- API support added
- Tests added for this feature/bug
- Has been reviewed by UX
- Has been reviewed by Frontend
- Has been reviewed by Backend
- Has been reviewed by Database
- Conform by the merge request performance guides
- Conform by the style guides
- Squashed related commits together
- Internationalization required/considered
- If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
What are the relevant issue numbers?
Closes #3947 (closed)