feat: prerelease/RC versioning

[decofe]

Support prerelease versions for release candidate workflows.

changelogs version --prerelease rc

Should bump e.g. v1.6.0 → v1.6.0-rc1, then v1.6.0-rc2 on subsequent runs. Running changelogs version without the flag promotes to stable (v1.6.0).

The GitHub Action should accept a prerelease input that passes this through.

Needed for foundry-rs/foundry which uses RC releases before stable.