release: add release:close, rename release:publish to release:stage
Created by: bobheadxi
Closes https://github.com/sourcegraph/sourcegraph/issues/14912 with a new release:close
announcement command (mostly a convenience for now, but can possibly attach more automation to this in the future)
To avoid confusion, rename release:publish
to release:stage
(since it just opens PRs, so is more a stage than a publish anyway)