automatically maintain a changelog when creating a release

[andreineculau]

• https://github.com/git-chglog/git-chglog - does the job, needs some new files getting committed into each repo, primary worry is that it has some long standing issues, and not many users

• make unreleased https://github.com/tobiipro/support-firecloud/blob/ba2f2fc/repo/mk/core.misc.release.mk#L116-L142 - super simple, no dependencies

Two other alternatives are got a hell no:

• https://github.com/conventional-changelog/conventional-changelog/tree/master/packages/conventional-changelog-cli - is an npm package, both heavy and dynamic, not a good choice for smth language agnostic like support-firecloud

• https://github.com/github-changelog-generator/github-changelog-generator - it's a ruby gem, alternatively running inside a docker container, but needs a github personal access token, and didn't run out of the box