Limit label dropdown choices in issues and mr dashboard view
- In the issues and mr dashboard view of GitLab (i.e. for GitLab.com it would be, https://gitlab.com/dashboard/issues and https://gitlab.com/dashboard/merge_requests), when clicking the dropdown for Labels, we should restrict the options so as to maximize performance.
- The label choices should be limited to whatever choices have already been made in the other three columns. For example, if the assignee has been chosen to a particular person, only the labels associated with the issues assigned to that person should appear in that dropdown. We don't need to present other labels to the user.