'swh' being the new master command group (defined in swh.core); so:
swh deposit --help
works. The 'admin' (deposit server management) is only available if the
swh.deposit[server] optional package is installed.
Ensure the 'swh-deposit' still works for now.
Related to T1671
also rename the 'deposit' subcommand as 'upload'
to prevent the ugly 'swh deposit deposit' in favor of:
swh deposit upload
Depends on D1426.