Apply --rc automatically on release branches #239
Description
auto-changelog validate has an --rc mode which validates that a section for the specified version is present in the changelog, and that the Unreleased section is empty. This is useful (as the name implies) for a release candidate, where a new version is being released. Similarly, auto-changelog update --rc will copy over changes in Unreleased to the specified version so as to pass validation.
However, needing to sometimes pass --rc and sometimes not complicates how changelogs are validated. It means that that in projects that use auto-changelog, the changelog validation step in yarn lint and in the build-lint-test workflow must check for whether the current branch is a release branch and add --rc appropriately. It would be nice not to have to do this, and if instead, auto-changelog could detect whether or not it is being run on a release branch and grab the current version from package.json automatically.