RHEL blocks users from executing crontab as themselves Because Of Reasons so we need to use sudo instead.
Also refactors file writing to properly support writing the permissions on sudoers files going forward.
Closes#5020
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
