Fix several issues with the Sentry file uploads which prevented Sentry
from using the uploaded files.

 - Upload the JS bundles to Sentry as well as the sourcemaps. Sentry
   reads the `sourceMappingURL` comment from the JS

 - Set the correct URL prefix for the files, so that Sentry knows that
   eg. "sidebar.bundle.js" is served at https://cdn.hypothes.is/hypothesis/$VERSION/build/scripts/sidebar.bundle.js

   For Sentry to use a file uploaded in a release, the artifact name
   (URL prefix + name) must match the URL from which it is served (and
   referenced in crash reports). The origin of the URL can optionally be
   shortened to `~`, but we haven't done that here.

 - Finalize the release after uploading files