Deeply Nested Subcommand Scripts

[Nekroze]

Is your feature request related to a problem? Please describe.
Currently subcommands are scripts in a single directory even though there are now many nested subcommands, this has made the scripts bloated and hard to grok/read/refactor.

Describe the solution you'd like
Allow directories under app/subcommands to become subcommand namespaces like dab repo is that does nothing but provide info and access to other subcommands represented by scripts in that directory.

Continuing with the repo example, app/subcommands/repo.sh would become something like app/subcommands/repo/{entrypoint,group,manage}.sh which would require the current repo add top level repo sub subcommands to be moved to something like manage.

Describe alternatives you've considered
Could rewrite in a different language that allows better composition, too big of an increment though.

Additional context
N/A.