release: generate GitHub release on release:close
Created by: bobheadxi
Updates the release tool to generate a proper GitHub release on the release:close
step, which allows folks to use the "watch releases" feature on GitHub to be notified of releases.
The release includes a link to the changelog, update guide, and release post. The generated release gets linked to from the final tracking issue update and Slack announcements.
Closes https://github.com/sourcegraph/sourcegraph/issues/13598 (see issue for more details!)