Editorial Metadata - filter and search based on metadata

## Expected/Desired Behavior

When viewing Edit Flow Editorial Metadata, I'd like to view all posts within a selected taxonomy (similar to tags & categories). I do not want the taxonomy to be viewable on the published posts.

Current: https://cloudup.com/cnfVU452AX0
Wishlist: https://cloudup.com/ceSoCFSu54T (link to view all posts that have the taxonomy)

Goal: provide a link to one person willing to audit all posts on Learn that need code snippet proofreading, or another to a person interested in resolving broken image links.

## Actual Behavior

How does the plugin/feature/module currently work.
The only way to view all posts with the custom editorial metadata taxonomy is to publish the taxonomy to the visible front-end.

Start by reproducing the Editorial Metadata workflow described in the issue and compare the current behavior with the wishlist screenshots. Trace how the custom taxonomy is exposed in the editor and on published posts; done means editors can filter or search posts by the taxonomy while it remains hidden from the public frontend.

Written by the indexing model from the issue text.