Rework Quantity parsing

[Techassi]

Our custom Quantity parsing doesn't match K8s behavior completely. This issue tracks the improvement of our parsing. This might break tests.

Parsing spec: https://kubernetes.io/docs/reference/kubernetes-api/common-definitions/quantity/

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This issue was raised after an internal arch meeting where the code style around resource specifications was discussed.

Acceptance criteria

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1. tests are added that cover the current mismatch in parsing
2. the parsing is fixed and in sync with k8s parsing
3. quantity format document in the documentation is updated

See

• https://github.com/orgs/stackabletech/discussions/60
• MemoryQuantity parsing fails when unit is missing community#61