Support poetry prerelease

[mattiasliljenzin]

Would be great to support prerelease versions for kacl. Maybe there's a workaround somewhere?

$ poetry version prerelease
Bumping version from 0.0.1 to 0.0.2a0

$ poetry run kacl-cli release 0.0.2a0
Error: "0.0.2a0" not a valid semantic version.