test: add utility for namespace labels patching and add the test cases for denyNodeFeatureLabels restriction

[TessaIO]

Resolves #1879

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[TessaIO]

/cc @marquiz
Maybe we can add this for v0.17 also

[marquiz]

I think it would make sense to specify these in pkg/utils/jsonpatch.go

Again, this could be a separate PR converting all uses of utils.NewJsonPatch to use these definitions.

WDYT?

Also, bike-shedding on the naming, for the generic pkg/utils version:

Suggested change

	AddOperation = "add"
	RemoveOperation = "remove"
	JSONPatchOpAdd = "add"
	JSONPatchOpRemove = "remove"