Switch to Conventional Commits

[adutra]

See https://www.conventionalcommits.org/en/v1.0.0 for the spec.

• Add note to CONTRIBUTING.md
• Add GitHub Actions workflow to check PR commits
• Check automatically generated releases

[adutra]

Other ideas:

• pre-commit hook: https://github.com/compilerla/conventional-pre-commit
• changelog generation: https://github.com/conventional-changelog/conventional-changelog
• linter: https://github.com/conventional-changelog/commitlint

[adutra]

Actions available:

• https://github.com/marketplace/actions/conventional-commit-in-pull-requests
• https://github.com/marketplace/actions/verify-conventional-commits
• https://github.com/marketplace/actions/conventional-commits-action
• https://github.com/marketplace/actions/conventional-commit-checker