Enable parallel processing with crd-generator v2

[shawkins]

The v2 generator will need to be parallized at the clazz level.

There will need to be a ResolvingContext instance for each usage - the SchemaGenerator isn't thread-safe. But they could all share the "seen" Jackson schema instances so that any common classes would not need to be re-resolved.

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[baloo42]

I think this feature has already been implemented with #5949:

https://github.com/fabric8io/kubernetes-client/blob/main/crd-generator/api-v2/src/main/java/io/fabric8/crdv2/generator/CRDGenerator.java#L194

Parallel execution is also enabled by default in the maven plugin and in the CLI.

[shawkins]

@baloo42 looks like we're good to resolve this properly.