distro/rpm: improve %files section

* improve %doc macro usage
* remove excessive %{name} usage
* update %attr rights
  * 750 -> 770 on /etc/knot to enable includes from knot.conf
  * 775 -> 770 on /var/lib/knot which can contain sensitive stuff
  * ___ -> 770 on /run/knot
* don't list /var/lib/knot/keys which is created dynamically
* remove duplicate entry
* fix incorrect whitespace