Show issues I :star:ed

Solution and design

• In the issues list view, see only the issues I have ⭐ ed, probably using the search bar filter.
• The UI does not need to solve more complex cases such as somebody else's ⭐ ed issues. That can be a stretch goal. But the UI should make it easy to default to my issues.
• Design may be similar to what is already shown here: https://gitlab.com/gitlab-org/gitlab-ce/issues/27754

Problem

Sometimes, people want to 'star' an issue or otherwise mark it, but just for themselves. There isn't really a good way of doing this:

• Labels affect everyone on the issue, and adding my personal smcgivern label to every project would be really dumb. (Also https://gitlab.com/gitlab-org/gitlab-ce/issues/21194.)
• Use a text file / Google Doc / whatever. This is what I do, but it's also dumb because I don't have an easy way to see if any of those issues were closed without opening them all manually.
• Just keep the tabs open.

My proposal is: we could let you see a list of issues / MRs (like the todo list) that only contains issuables you awarded the ⭐ emoji to. That way, ⭐-ing an issue has more value than just a social signal, and also acts like a bookmark / favourite / star.

Advanced mode could be show all issues you've awarded an emoji to, and allow filtering by the emoji, but even ⭐ would be a good start.