"Resolve" functionality for issues

Problem to solve

Big issues with lots of comments are very hard to read and keep track. Those issues can live for months gathering comments that are not relevant anymore or was already included in issue description or moved out to a separate issue. But these comments are still piled up at the issue.

Intended users

All gitlab users, especially users who prepare issues for development.

Proposal

We can add Resolve functionality to gitlab issues too (same as we have for MRs) so people can mark discussion thread as resolved when they took all required actions.

Example of resolved threads: !26891 (comment 302735982)

Permissions and Security

Same as MR "Resolve discussion" functionality

Links / references

Release Notes

Long-running issues with many threads can be challenging to read and track. You can now resolve a thread on an issue when the topic of discussion has concluded.

https://docs.gitlab.com/ee/user/discussions/#resolve-a-thread