Validation of immutable fields, passing oldResource from admission request

[jonesbusy]

https://github.com/operator-framework/josdk-webhooks/blob/main/core/src/main/java/io/javaoperatorsdk/webhook/admission/validation/Validator.java takes only the current resource for validation

Shouldn't we be able to retrieve the oldResource on https://github.com/operator-framework/josdk-webhooks/blob/main/core/src/main/java/io/javaoperatorsdk/webhook/admission/validation/DefaultAdmissionRequestValidator.java#L27 for validation

So that we can validate immutable field between the oldResource and the current resource?