switch headings from settext to atx

howto/backup.md

howto/drbd.md

howto/grafana.md

howto/ipsec.md

howto/kvm.md

howto/logging.md

howto/nagios.md

howto/openstack.md

howto/postgresql.md

howto/prometheus.md

howto/static-component.md

service/schleuder.md