`yardstick label explore ...` should provide way to focus on unlabeled matches

**What would you like to be added**:

When I run `yardstick label explore ` I should be able to quickly find any matches that are not labeled.

**Why is this needed**:

Otherwise, when labeling results for an image with a lot of matches, many of which are already labeled, searching for unlabeled matches involves a lot of additional scrolling.

**Additional context**:

Start with the `yardstick label explore ` CLI entry point and trace how matches are displayed and labels are handled. Add a way to focus the results on unlabeled matches, and verify that labeling workflows can find those matches without scrolling past already labeled results.

Written by the indexing model from the issue text.