releases: investigate different method of generating changelog

Feature Request

Describe the problem you need a feature to resolve.

Currently, the changelog is generated from changelog/fragments in CHANGELOG.md, and soon to be in changelog/generated/<version>.md. The changelog and deleted fragments need to be committed in a release commit. Ideally this release commit would either be smaller or non-existent, which implies that the changelog be committed in some other way or not at all.

Describe the solution you'd like.

My main suggested solution is to use goreleaser's default changelog generator. This means that we'll have to start enforcing a commit message structure, which I think is a reasonable thing to do, and helpful regardless of whether we generate a changelog from them or not.

/kind feature