ci: use semi-automated release & post-release actions

[kelly-sovacool]

Changes

• The draft-release action is run on manual dispatch, using the latest commit from whichever branch you select. It detects the next version, updates the changelog, citation, and version files, and creates a draft release. You can then view the proposed tag, make any edits, and manually publish the release.
• The post-release action runs automatically after you publish a release. It updates the changelog and version files for the development version, creates a branch release-${tag} (with the version tag), and opens a pull request with these changes. It also deletes the release-draft branch during cleanup.

Requirements

• The files CHANGELOG.md, VERSION, and CITATION.cff must exist in the top level of the repo.
• CHANGELOG.md must contain a header containing the string 'development version', and this should be the first header in the file. It's crucial to update the changelog with every PR that contains user-facing changes as these become the release notes for the next version.

Issues

NA

PR Checklist

(~Strikethrough~ any points that are not applicable.)

• [x] This comment contains a description of changes with justifications, with any relevant issues linked.
• ~[ ] Update docs if there are any API changes.~
• ~[ ] Update CHANGELOG.md with a short description of any user-facing changes and reference the PR number. Guidelines: https://keepachangelog.com/en/1.1.0/~ [these changes are not user-facing]

[kelly-sovacool]

We'll pilot this in a few release cycles of RENEE. If all goes well we can turn this into a reusable action and add it to our other repos too.