release: automate the update of the release-config file

Created by: coury-clark

The release tool reads much of it's configuration from a configuration file https://sourcegraph.com/search?q=context:%40sourcegraph/all+file%3Arelease-config+

This file has to be manually updated prior to each release. At the very least we schedule minor releases to a fixed schedule, to which we could automatically generate the updates and create a PR.