Add support for Cassandra 4.0 beta images

[emerkle826]

This should address #373

[jsanda]

@emerkle826 based on testing I have done thus far I think we can do without these changes. The validation already supports 4.0.0 for the version. I am able to use the beta4 image with that. Granted it makes it a bit less obvious which beta you are actually running but that can be ascertained from the image tag. The other, bigger benefit is that we wouldn't have to worry about config-builder changes to recognize (4\.0-beta\d+) in addition to 4.0.0.