feat: Implement Sum for CpuQuantity and MemoryQuantity

[sbernauer]

Description

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Definition of Done Checklist

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1. Changes are OpenShift compatible
2. CRD changes approved
3. Integration tests passed (for non trivial changes)

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1. Code contains useful comments
2. (Integration-)Test cases added
3. Documentation added or updated
4. Changelog updated
5. Cargo.toml only contains references to git tags (not specific commits or branches)

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1. Feature Tracker has been updated
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[maltesander]

Changelog entry? LGTM otherwise.

[sbernauer]

@maltesander thx for review, changelog added

[maltesander]

LGTM!