fix: Don't allow uppercase characters in Kubernetes object names

[xeniape]

Description

Follow up to #1064, which introduced uppercase characters in domain names. The updated format was used for domain names as well as container names in Kubernetes for example. But, actually, the Kubernetes RFC 1123 specification is slightly different, only allowing lowercase characters, see https://kubernetes.io/docs/concepts/overview/working-with-objects/names/#dns-label-names. This PR adjusts the separation of usage between the two.

Definition of Done Checklist

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Author

• Changes are OpenShift compatible
• CRD changes approved
• CRD documentation for all fields, following the style guide.
• Integration tests passed (for non trivial changes)
• Changes need to be "offline" compatible

Reviewer

• Code contains useful comments
• (Integration-)Test cases added
• Changelog updated
• Cargo.toml only contains references to git tags (not specific commits or branches)

Acceptance

• Feature Tracker has been updated
• Proper release label has been added

[siegfriedweber]

LGTM