pkg/utils: Support Fedora rawhide version name
Since pulling the Fedora Rawhide image from registry.fedoraproject.org/fedora/rawhide succeeds now, add support for the Fedora Rawhide version name by allowing rawhide to be passed as a release argument.
Fixes: #646.
Build succeeded. https://softwarefactory-project.io/zuul/t/local/buildset/41cf57212d864d5d95f775fced8570cc
:heavy_check_mark: unit-test SUCCESS in 5m 12s :heavy_check_mark: unit-test-migration-path-for-coreos-toolbox SUCCESS in 3m 32s :heavy_check_mark: unit-test-restricted SUCCESS in 5m 11s :heavy_check_mark: system-test-fedora-rawhide SUCCESS in 1h 30m 39s :heavy_check_mark: system-test-fedora-40 SUCCESS in 1h 28m 16s :heavy_check_mark: system-test-fedora-39 SUCCESS in 1h 30m 51s
Closing as stale. Feel free to reopen if needed.