Need a 'class/group' field in the user credentials

[dhilipkr]

As part of user accounts under AuthorizedKeysRequest->AccountCredentials and AuthorizedUsersRequest->UserPolicy, a 'class' field is required to ADD a "new" user account. The 'class' field is of type string that defines a class name. The 'class' is used to associate the user account with the 'class'. The 'class' defines the permissions for the 'user' account. In order to handle "new" user account creation with a 'credentials' configuration pushed through bootz (bootz.proto), a user 'class' is required. Or an acceptable default 'class' will have to be used, where the "default" class has the necessary permissions that can be applied to all user accounts created through RPCs via gnsi-credentialz. Request is to make provision in credentialz.proto to be able to specify a user 'class' under "AccountCredentials" and "UserPolicy".