Release Process Enhancement

To avoid multiple manual tasks (release prep, resetting notes, creating GH releases, etc) per release, we need to make some changes to the process.

For the short term (no automation yet), we will add a `changelog.md` file to each location a `release_notes.md` file exists. During release prep, changes will be moved from `release_notes.md` to `changelog.md` as a new version entry, and `release_notes.md` will be released.

Tasks:

- [ ] Add `changelog.md` for each package we release
- [ ] Investigate ways to automate the release process (automate updating changelog and resetting release notes)

Start by locating every package directory that contains a release_notes.md file and review how release preparation currently handles those files. Add a changelog.md beside each applicable release_notes.md, then document or prototype a way to move entries, reset release notes, and create GitHub releases. Done means all released packages have the expected files and the release steps are repeatable.

Written by the indexing model from the issue text.