Add "controllerutil" helpers for applyconfigurations (SSA)

We are making extensive use of the helpers defined in https://github.com/kubernetes-sigs/controller-runtime/blob/main/pkg/controller/controllerutil/controllerutil.go, and while migrating our controllers to SSA we had to create our own modified copies based on corev1/metav1 applyconfigurations.

I think it could make sense adding a SSA-flavoured edition of these simple (but useful) helpers to controller-runtime. And I would be happy to submit a PR if you agree. The most challenging is probably to decide the package name/location. WDYT @alvaroaleman @vincepri @sbueringer?

Start by reading pkg/controller/controllerutil/controllerutil.go and the referenced corev1/metav1 applyconfigurations. Review the discussion to determine whether controller-runtime should add SSA-flavoured helpers and where they belong; done requires agreement on the package location and scope before implementation.

Written by the indexing model from the issue text.