fix(controller): inject config on top of existing environment
fix(controller): do not commit to latest

while this was a nice-to-have before, we are actually pushing config
values on top of the latest build, which breaks config:unset.
fix(controller): use build tag if present
Merge pull request #2127 from bacongobbler/2100_env_in_dockerfile

fix(controller): inject config on top of existing environment