Support `PrimaryToSecondaryMapper` in KubernetesDependnetResource

[csviri]

In similar way the SecondaryToPrimaryMapper is supported.

see: https://github.com/java-operator-sdk/java-operator-sdk/blob/3e4723a36f6a08639b7d7903ae4847a63de20e42/operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/dependent/kubernetes/KubernetesDependentResource.java#L87-L89

[csviri]

Now I'm thinking if this makes sense for dependent resources. PrimaryToSecondaryMapper is only needed if there is a many-to-one or many-to-many relationship between the secondary and primary resource. That mean those resources are usually not managed, just serves as an input. So there is no need to create a dependent resource for them, rather that would be just an informer to have them cached.

Will close this issue until, we receive a concrete use-case / request for this.

[csviri]

Note that this might be beneficial in the case if some want to add a reconcile pre-condition on a read only resource. So I'm reopening this issue.

[csviri]

Added sample how this is possible to do.