Expose revision_log_by in client and server

Currently, the function revision_log_by is implemented in storage but is exposed neither in the client nor the server. Wondering if it's intentional, and if not, if we could expose it correctly. It's useful to avoid making an extra request to the database in the web ui when looking for a revision with origin, probably among other things.

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Migrated from T432 (view on Phabricator)