USB access

Even with `-v /dev/bus/usb:/dev/bus/usb` I have to set `--user root` and `-e USER=root` to list connected ledgers 🤔 Perhaps add the `tezos` user to `plugdev` group? That is the group which gets privileges by the default `add_udev_rules.sh` script.

Inspect the Dockerfiles and the referenced add_udev_rules.sh script, then reproduce USB ledger access with the /dev/bus/usb volume as the default tezos user. Compare the container's group membership and the permissions established by the udev rules; done means connected ledgers can be listed without --user root or USER=root.

Written by the indexing model from the issue text.