Add support for setting uidNumber for machine accounts

Giving computers (machine accounts) access to shares on a samba domain members requires that

• computers have the uidNumber attribute set
• The Domain Computers group has the gidNumber attribute set according to https://lists.samba.org/archive/samba/2017-November/212271.html

It would be nice if ADMan could set the uidNumber attribute for computers as we currently have to set this manually which seems a bit painful.