ci: Refactor release workflow

[samuelburnham]

Switches to composite release actions using argumentcomputer/ci-workflows#76.

Behavior is updated in several ways:

• Checks out the latest corresponding release branch as the basis for major and minor releases, where before it would always check out dev. This enables a streamlined release workflow where the maintainer opens the release PR, then cherry-picks the desired changes from dev that have been added since the last release, then pushes them to the release-pr branch for CI and review.
• Renames hotfix releases to patch in order to align with SemVer
• Adds a configurable changelog config, which separates PRs by label for easier viewing
• Various bug fixes and simplifications
• Improves support for tag prefixes in branch names and GitHub releases, e.g sphinx in release/sphinx-v1.0

Successful runs:

• chore: Release 3.6.0 samuelburnham/sphinx#31
• https://github.com/samuelburnham/sphinx/releases/tag/sphinx-v3.6.0

TODOS:

• Refine changelog categories in tag-release.yml, and factor them out into a .github/changelog-config.json file

Note

To be merged after argumentcomputer/ci-workflows#76