Additional groups - delete if a group already exists

[lholota]

Either by gid or by a name

When restarting container, the script throws error because the group already exists - it should skip creating the group if a group with the same gid already exists and has the same name. If name differs, delete and recreate.

Create a re-usable ash script and put it into /usr/sbin so that other images can reuse the functionality (e.g. certbot is creating an additional group for the cert reader)