logging: clean and consistent messages for zones

src/knot/nameserver/axfr.c

src/knot/nameserver/axfr.h

src/knot/nameserver/internet.c

src/knot/nameserver/ixfr.c

src/knot/nameserver/notify.c

src/knot/nameserver/process_query.h

src/knot/zone/events.c

src/knot/zone/zone.c