- Add the client version to the config so that we can rule out problems
   in the sidebar app because caused by a mismatch between the version
   of the client used in the annotator and the version used in the
   sidebar app.

 - Add the host URL to the config so that we can tell in Sentry reports
   which page embedded the client. Sentry reports currently have
   `document_url` metadata that is set using `document.referrer` in the
   sidebar app, but this gets truncated to the origin in some browsers.