Add group filter to merge request dashboard
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### Release notes
In the merge request dashboard there are many search filters you can apply, author, reviewer, deployed-before, etc. I would like to have "Group" and "Project" added to that list. It would be useful to be able to search for these when trying to sort through a very large list of MR's. Project isn't as useful as Group, since project can be searched while in the project, but it's more clicks the right from the dashboard.
### Intended users
Anyone who spans multiple groups/projects would benefit.
### Permissions and Security
Permissions would only be enforced on the search results level. if the user has no access, don't show it.
issue