Use CONTAINER_TOOL in catalog and bundle targets

The catalog-build and bundle-build targets did not respect the
CONTAINER_TOOL variable for selecting the container backend (docker
vs podman). Update both targets to use CONTAINER_TOOL (docker is still
the default one -> nothing changes in terms of the default behavior).

Author: lpiwowar

Makefile

@@ -336,7 +336,7 @@ bundle: manifests kustomize operator-sdk ## Generate bundle manifests and metada
 
 .PHONY: bundle-build
 bundle-build: ## Build the bundle image.
-	docker build -f bundle.Dockerfile -t $(BUNDLE_IMG) .
+	$(CONTAINER_TOOL) build -f bundle.Dockerfile -t $(BUNDLE_IMG) .
 
 .PHONY: bundle-push
 bundle-push: ## Push the bundle image.
@@ -373,7 +373,7 @@ endif
 # https://github.com/operator-framework/community-operators/blob/7f1438c/docs/packaging-operator.md#updating-your-existing-operator
 .PHONY: catalog-build
 catalog-build: opm ## Build a catalog image.
-	$(OPM) index add --container-tool docker --mode semver --tag $(CATALOG_IMG) --bundles $(BUNDLE_IMGS) $(FROM_INDEX_OPT)
+	$(OPM) index add --container-tool $(CONTAINER_TOOL) --mode semver --tag $(CATALOG_IMG) --bundles $(BUNDLE_IMGS) $(FROM_INDEX_OPT)
 
 # Push the catalog image.
 .PHONY: catalog-push