Add a filter to display MR's with unresolved comments
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### Release notes
Add in a filter to only display MR's in the list view with unresolved comments so that a user can see MR's which actively need work done.
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### Problem to solve
As a developer, I want to be able to filter down to MR's which only have unresolved comments so that I can easily identify which MR's actively need work.
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### Intended users
Developers
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### User experience goal
With a significant amount of MR's, it is increasibly harder to identify which ones actively need work done on them. This feature resolves this problem by allowing a user to search for MR's which have unresolved comments that need addressing.
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### Proposal
My main suggestion would be to add in a filter to the search bar so a user can type something like:
`unresolved-comments {OP} {int}` where OP can be `greater than`, `less than` or `equals`.
However if you want to make the change more generalised, and not just focused on unresolved comments, you could also add ones for `resolved-comments` or just `comments` in general. Though with the last one, I don't see much of a purpose to it if you have a filter for both `resolved` and `unresolved` comments.
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### Further details
Currently, on the MR list view, it shows you all the comments in an MR:

There is currently no way to see whether those three comments are resolved or not. So I have to click on the MR then view the top right to see if the comments are resolved.

It is tedious to do so, especially if you have a significant amount of MR's open.
There was an issue created over six years ago asking for this, but it was on the read-only repo [here](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/36612). Not sure if this is in the wrong place, I wanted to bump the issue but am unable due to the repo being read only.
Also apologies if this is all incorrect, I was just following the guide [here](https://gitlab.com/gitlab-org/gitlab/blob/master/doc/development/contributing/issue_workflow.md#feature-proposals).
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### Permissions and Security
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