Add support for additional release types: automation, documentation

[jefflinse]

Some merges to main are from things like dependabot merging dependency change to main, or from developers merging documentation changes that don't actually affect a codebase. Should consider supporting these scenarios in order to better determine how to proceed in such cases.

[jefflinse]

These dependabot merges demonstrate where there's room for improvement here:
https://github.com/jefflinse/pr-semver-bump/releases/tag/v1.1.1
https://github.com/jefflinse/pr-semver-bump/releases/tag/v1.1.2