cassandradatacenter_types: allow 1length rack name

[frivoire]

What this PR does: allow more flexibility in the naming of rack by allowing names with only 1char.

Rationale: on cloud-environments (ex: when using GoogleCloudSnitch for my use-case) & using the simple mapping: datacenter=cloudProvider-region & rack=cloudProvider-zone, we want to define just a, b, c as rack name, which is not possible today. AFAIK, this is mainly impacting when we have some existing clusters (created outside of the operator, with 1long rack names) and we want to migrate to the operator (using the same rack-name for a safe migration)

NB: the reason for this "min 2" is unclear to me, I only found the commit that introduced it but no explanation

Which issue(s) this PR fixes: no issue created

Checklist

• [ ] Changes manually tested => nothing tested 😆
• [ ] Automated Tests added/updated
• [ ] Documentation added/updated
• [ ] CHANGELOG.md updated (not required for documentation PRs)
• [ ] CLA Signed: DataStax CLA

[github-actions[bot]]

No linked issues found. Please add the corresponding issues in the pull request description.
Use GitHub automation to close the issue when a PR is merged

[burmanm]

Hey, thanks for the PR. I'll try to investigate if there was a reason why the restriction was 2.