I'd like to second Kustomize. It's not getting enough popularity, IMO. It's also great because it doesn't break tooling by mixing in a templating language on to

I'd like to second Kustomize. It's not getting enough popularity, IMO. It's also great because it doesn't break tooling by mixing in a templating language on top of a configuration language. If people need more than Kustomize supports, there's always Cue or Pulumi; I'd never recommend Helm, personally.