This change minimizes the work needed to be done when tagging images. It edits the image manifest directly only when necessary, allowing restarts of an app to avoid having an extra layer.
This also additionally allows to deploy images with ONBUILD directives without running the ONBUILD directives.
Lastly, users building docker images that run Dokku will need to use a new sudoer wrapper for the `docker-image-labeler` binary to work correctly. A reference version has been placed in the `docker` skeleton directory.
Closes#3931
Refs #4226
This change adds a new builder - builder-cnb - via the 'DOKKU_CNB_EXPERIMENTAL' environment variable. While support for customizing pack builds is not currently implemented and there may be other missing functionality, this initial implementation allows folks to start playing with CNB.
Future releases of Dokku will provide tighter CNB integration and eventually switch to CNB for default building, as well as allow users to better select builders needed for their applications.
All new code for CNB support should be considered experimental and subject to change as the support evolves over time.
