This makes standard use of shellcheck work without needing to provide extra configuration anywhere.
Also remove use of inline 'shellcheck disable' calls that are already defined in the .shellcheckrc and don't need to be set inline.
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.
This functionality was broken due to a refactor of argument handling in a previous release.
In addition to the fix, all the functionality was moved to scheduler-enter, which allows scheduler plugins to implement ways of entering containers in the relevant scheduler.
Closes#3972
