Feature Request: add substitute-from flag #979
Description
currently i am using https://github.com/xunholy/fluxcd-kustomize-mutating-webhook to dynamically add postbuild substitutions from a "global" configmap for all kustomizations, this allows me to centralize my variable configuration while allowing me to define kustomizations in any namespace. Unfortunately this means that from flux-local's perspective, I don't have and substitutions, this starts to cause errors when these substitutions are in path's or url's i.e. ${IMAGE_REGISTRY}.
what i would like to see added, is a flag, called something like --substitute-from that could point to a definition of a configMap, and those values be side-loaded into the post build substitutions during rendering