Add labels to Registry search results (capped by configurable # of labels to return per item)

[EricWittmann]

The idea here is to include labels for Groups, Artifacts, and Versions in search results for those entities. We don't do that now because the # of labels is unbounded, and it's not great practice to return an unbounded collection in a REST API response, let alone an unbounded number of items per search result item.

So we're going to return labels, but we'll cap the # of labels per item. The cap will be globally configurable via an ENV var.

[EricWittmann]

Duplicate of: #5219

[EricWittmann]

Closing as duplicate.