Line up $IMG in Makefile with convention

This changes the value of $IMG in the Makefile to line up with other
GitOps toolkit controllers. The main effect is the the `kustomize edit
image` commands used in the deploy and dev-deploy targets will now set
the image tag, rather than let it stay at whatever the last release
was.

Signed-off-by: Michael Bridgen <[email protected]>

Author: squaremo

Makefile

@@ -1,5 +1,5 @@
 # Image URL to use all building/pushing image targets
-IMG ?= fluxcd/image-automation-controller
+IMG ?= fluxcd/image-automation-controller:latest
 # Produce CRDs that work back to Kubernetes 1.16
 CRD_OPTIONS ?= crd:crdVersions=v1