Merge branch 'catalog_gen_groups' into 'master'

doc/man/knot.conf.5in

doc/reference.rst

src/knot/catalog/catalog_update.c

src/knot/catalog/generate.c

src/knot/conf/schema.c

src/knot/conf/schema.h

src/knot/conf/tools.c

src/knot/conf/tools.h

src/knot/zone/zone-dump.c

src/knot/zone/zone.h

src/knot/zone/zonedb-load.c

tests-extra/tests/catalog/gen_groups/test.py

tests-extra/tools/dnstest/server.py