[ENHANCEMENT] Load KubeVirt relevant CRDs elegantly while running tests

[starbops]

In order to test the virtualmachine-controller's behavior, we brutally download the KubeVirt API repository and generate the CRD manifests in the generate-kubevirt-crd target and make it a dependency of the test target:

.PHONY: generate-kubevirt-crd
generate-kubevirt-crd: controller-gen ## Clone KubeVirt API and generate CustomResourceDefinition objects for integration testing purposes.
	TMP_DIR=$$(mktemp -d -p /tmp/); \
	KUBEVIRT_API_DIR=$$TMP_DIR/kubevirt-api; \
	git clone --depth 1 --branch $(KUBEVIRT_API_VERSION) https://github.com/kubevirt/api $$KUBEVIRT_API_DIR; \
	$(CONTROLLER_GEN) crd:allowDangerousTypes=true paths="$$KUBEVIRT_API_DIR/core/v1/..." output:crd:artifacts:config=config/kubevirt-crd; \
	rm -rvf $$TMP_DIR; \
	rm -vf config/kubevirt-crd/kubevirt.io_datavolumetemplatespecs.yaml
...
.PHONY: test
test: manifests generate generate-kubevirt-crd fmt vet envtest ## Run tests.
	KUBEBUILDER_ASSETS="$(shell $(ENVTEST) use $(ENVTEST_K8S_VERSION) --bin-dir $(LOCALBIN) -p path)" go test ./... -coverprofile cover.out

That's because we need those KubeVirt CRD manifests to be loaded when setting up the test environment for testing the virtualmachine controller:

	testEnv = &envtest.Environment{
		CRDDirectoryPaths: []string{
			filepath.Join("..", "..", "..", "config", "crd", "bases"),
			// TODO: This requires collaboration from Makefile to pull down the
			// api repo and generate CRD objects beforehand. It should be
			// possible to leverage the CRD option to import CRD objects
			// directly instead of adding them from directories.
			filepath.Join("..", "..", "..", "config", "kubevirt-crd"),
		},
		ErrorIfCRDPathMissing: true,
		BinaryAssetsDirectory: filepath.Join("..", "..", "..", "bin", "k8s",
			fmt.Sprintf("1.28.0-%s-%s", runtime.GOOS, runtime.GOARCH)),
	}

This could be done in a more elegant way. Currently, I'm not sure how, but there's a CRD field in envtest.Environment (godoc) that we can leverage (perhaps):

	// CRDs is a list of CRDs to install.
	// If both this field and CRDs field in CRDInstallOptions are specified, the
	// values are merged.
	CRDs []*apiextensionsv1.CustomResourceDefinition