kuberesource: use common labeling strategy

[burgerdev]

This PR centralizes the definition of labels and label selectors, which used to be ad-hoc. As a result, labels for individual API resources may differ after this change, but the labels should at least be consistent.

[sespiros]

Thanks! Should we mark this as a breaking change, or at least add a note? Since an in place upgrade (albeit not a documented procedure) would not be possible since we are changing the label selectors on Contrast-managed resources?

[davidweisse]

Should this also use kuberesource.SelectorLabels("kvstore", "coordinator")?

[burgerdev]

Ok, it turns out that this selector is worth than useless, since we're already filtering by name and we don't set the label in RecoverConfigMaps. Removing it here, fixing RecoverConfigMaps in #2515.

[burgerdev]

Thanks! Should we mark this as a breaking change, or at least add a note? Since an in place upgrade (albeit not a documented procedure) would not be possible since we are changing the label selectors on Contrast-managed resources?

It's marked as changelog. The only thing where this matters would be the ConfigMap watcher, which was using the same label selector until I just changed it due to @davidweisse's remark. Let me revert that change for now, maybe I'll come up with something in #2515.