Allows using `--debug` to enable debug logging under
any subcommand. Currently it needed to be set as
`docker --debug buildx` meaning only way to enable debug
in standalone mode was to set env variable instead and
updating existing commands to add `--debug` was cumbersome.
Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
Prior to this commit, experimental flags were not distinguishable from
regular flags in `--help`
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
