RPM: Add new subpackage for PAC responder
    
    It was discovered that duplicating files in two subpackages is not
    permitted by Fedora packaging guidelines[1]. This patch moves the PAC
    responder to a new sssd-common-pac subpackage that both the sssd-ipa
    and sssd-ad subpackages will require.
    
    [1] https://fedoraproject.org/wiki/Packaging:Guidelines?rd=Packaging/Guidelines#DuplicateFiles