env variable substituion for koki short server #138

The current env variable substitution for the short server is done imperatively, and the results are substituted into the file server/deployment.short.yaml

It would be better if the definition of the env resources was done declaratively, and the only imperative step is the substitution.

The best case scenario is where everything is declarative - this can be achieved by setting the secretive env vars into a secret resource, and then the env variable could be inferred from secret.