Makefile: add clean target (opendatahub-io#733)

Add `make clean` which removes build artefacts. At the moment it's
./bin, ./odh-manifests/* and cover.out from test target.

Do not remove odh-manifests directory since it is commited to VCS.

In the recipe chown of $(LOCALBIN) since setup-envtest makes its dir
RO for some reason [1].

Related: opendatahub-io#696

[1] https://github.com/kubernetes-sigs/controller-runtime/blob/main/tools/setup-envtest/store/store.go#L191

Signed-off-by: Yauheni Kaliuta <ykaliuta@redhat.com>

Makefile

@@ -149,6 +149,7 @@ lint: golangci-lint ## Run golangci-lint against code.
 .PHONY: get-manifests
 get-manifests: ## Fetch components manifests from remote git repo
 	./get_all_manifests.sh
+CLEANFILES += odh-manifests/*
 
 ##@ Build
 
@@ -198,6 +199,7 @@ undeploy: ## Undeploy controller from the K8s cluster specified in ~/.kube/confi
 LOCALBIN ?= $(shell pwd)/bin
 $(LOCALBIN):
 	mkdir -p $(LOCALBIN)
+CLEANFILES += $(LOCALBIN)
 
 KUSTOMIZE_INSTALL_SCRIPT ?= "https://raw.githubusercontent.com/kubernetes-sigs/kustomize/master/hack/install_kustomize.sh"
 .PHONY: kustomize
@@ -315,7 +317,12 @@ test: unit-test e2e-test
 .PHONY: unit-test
 unit-test: envtest
 	KUBEBUILDER_ASSETS="$(shell $(ENVTEST) use $(ENVTEST_K8S_VERSION) --bin-dir $(LOCALBIN) -p path)" go test $(TEST_SRC) -v  -coverprofile cover.out
+CLEANFILES += cover.out
 
 .PHONY: e2e-test
 e2e-test: ## Run e2e tests for the controller
 	go test ./tests/e2e/ -run ^TestOdhOperator -v --operator-namespace=${OPERATOR_NAMESPACE} ${E2E_TEST_FLAGS}
+
+clean:
+	chmod u+w -R $(LOCALBIN) # envtest makes its dir RO
+	rm -rf $(CLEANFILES)