Allow pbs_ralter to edit Authorized_Users and Authorized_Groups

Users want to be able to edit the authorized users and groups of a reservation.

Design can be found here:

Will you do any verification that the requested group is valid?

It will be the same validation as when you set a group via pbs_rsub.

I’ve updated the design to also include unsetting the Authorized_Groups attribute. This can be done by using an empty string for the value of -G, for example, pbs_ralter -G “” R3.