Makefile: allow SETUP_FLAGS to be passed to shipperctl

Makefile

@@ -29,6 +29,9 @@ SHIPPER_CLUSTER ?= microk8s
 # ones).
 E2E_FLAGS ?=
 
+# Defines optional flags to pass to `shipperctl` when running `make setup`.
+SETUP_FLAGS ?=
+
 # When set, deployments generated by `make build-yaml` will refer to the
 # image's digest instead of a tag. Very useful in development, but not so much
 # when building releases.
@@ -77,7 +80,8 @@ KUBECTL ?= kubectl -n $(SHIPPER_NAMESPACE)
 setup: $(SHIPPER_CLUSTERS_YAML) build/shipperctl.$(GOOS)-amd64
 	./build/shipperctl.$(GOOS)-amd64 admin clusters apply \
 		-f $(SHIPPER_CLUSTERS_YAML) \
-		--shipper-system-namespace $(SHIPPER_NAMESPACE)
+		--shipper-system-namespace $(SHIPPER_NAMESPACE) \
+		$(SETUP_FLAGS)
 
 # Install shipper in kubernetes, by applying all the required deployment yamls.
 install: install-shipper install-shipper-state-metrics