search: log requests to honeycomb

Created by: keegancsmith

We want to explore every search done on sourcegraph.com in honeycomb. We hook into the existing logging we have. We could be logging a lot more (repos searched/etc), and more often (for example it seems errors and paginated search skip this). For now this is sufficient.

Best reviewed commit by commit.

Part of https://github.com/sourcegraph/sourcegraph/issues/13683