WIP: rename "samba-tool group add" command to "... create"
In the year 2011 the "samba-tool user add" command has been replaced by "create" and later (2016) the add command has been marked as deprecated. Volker mentioned in 2017 (I think on the mailing list), that we should also adapt the other samba-tool commands. Customers, myself and probably other users like to have a more "symmetric" set of commands.
I already start the merge request today as "WIP", because I would like to read your comments before I finish this.