Add Makefile and make options configurable

Signed-off-by: James Munnelly <james@munnelly.eu>

Makefile

@@ -0,0 +1,20 @@
+IMAGE_NAME := "webhook"
+IMAGE_TAG := "latest"
+
+OUT := $(shell pwd)/_out
+
+$(shell mkdir -p "$(OUT)")
+
+verify:
+	go test -v .
+
+build:
+	docker build -t "$(IMAGE_NAME):$(IMAGE_TAG)" .
+
+.PHONY: rendered-manifest.yaml
+rendered-manifest.yaml:
+	helm template \
+	    --name example-webhook \
+        --set image.repository=$(IMAGE_NAME) \
+        --set image.tag=$(IMAGE_TAG) \
+        deploy/example-webhook > "$(OUT)/rendered-manifest.yaml"