fix: Invalid CRD schema for StackableAffinity contents

[sbernauer]

Description

Fixup of #821

Before

The CustomResourceDefinition "druidclusters.druid.stackable.tech" is invalid: 
* spec.validation.openAPIV3Schema.properties[spec].properties[coordinators].properties[config].properties[affinity].default.podAffinity: Invalid value: "null": podAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[coordinators].properties[config].properties[affinity].default.podAntiAffinity: Invalid value: "null": podAntiAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[coordinators].properties[config].properties[affinity].default.nodeAffinity: Invalid value: "null": nodeAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[historicals].properties[config].properties[affinity].default.nodeAffinity: Invalid value: "null": nodeAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[historicals].properties[config].properties[affinity].default.podAffinity: Invalid value: "null": podAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[historicals].properties[config].properties[affinity].default.podAntiAffinity: Invalid value: "null": podAntiAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[middleManagers].properties[config].properties[affinity].default.podAntiAffinity: Invalid value: "null": podAntiAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[middleManagers].properties[config].properties[affinity].default.nodeAffinity: Invalid value: "null": nodeAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[middleManagers].properties[config].properties[affinity].default.podAffinity: Invalid value: "null": podAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[routers].properties[config].properties[affinity].default.podAffinity: Invalid value: "null": podAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[routers].properties[config].properties[affinity].default.podAntiAffinity: Invalid value: "null": podAntiAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[routers].properties[config].properties[affinity].default.nodeAffinity: Invalid value: "null": nodeAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[brokers].properties[config].properties[affinity].default.nodeAffinity: Invalid value: "null": nodeAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[brokers].properties[config].properties[affinity].default.podAffinity: Invalid value: "null": podAffinity in body must be of type object: "null"
* spec.validation.openAPIV3Schema.properties[spec].properties[brokers].properties[config].properties[affinity].default.podAntiAffinity: Invalid value: "null": podAntiAffinity in body must be of type object: "null"

After

customresourcedefinition.apiextensions.k8s.io/druidclusters.druid.stackable.tech created

Definition of Done Checklist

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Author

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

Reviewer

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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
2. Proper release label has been added

[NickLarsenNZ]

LGTM