implemented zone data backup

Knot.files

doc/man/knotc.8in

doc/man_knotc.rst

doc/operation.rst

src/knot/Makefile.inc

src/knot/ctl/commands.c

src/knot/ctl/commands.h

src/knot/dnssec/context.c

src/knot/dnssec/kasp/kasp_db.c

src/knot/dnssec/kasp/kasp_db.h

src/knot/dnssec/kasp/kasp_zone.c

src/knot/dnssec/kasp/kasp_zone.h

src/knot/events/events.c

src/knot/events/events.h

src/knot/events/handlers.h

src/knot/events/handlers/backup.c

src/knot/journal/journal_metadata.c

src/knot/journal/journal_metadata.h

src/knot/journal/knot_lmdb.c

src/knot/journal/knot_lmdb.h