feat(operator): Add Role::{fixed,estimated}_replica_count

[sbernauer]

Description

Needed for stackabletech/nifi-operator#953, we can then also use it in https://github.com/stackabletech/trino-operator/blob/3158402b23edde1633b2639eb50c67bb1b41889c/rust/operator-binary/src/crd/mod.rs#L918

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
• Code contains useful logging statements
• (Integration-)Test cases added
• Documentation added or updated. Follows the style guide.
• 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