dnstap: use the new type conversions API
dnstap: no need to report error on free
dnstap writer: assert instead of knot_unlikely
tests-extra: change zonefile-sync to 1 day to disable unwanted flush
kdig: refactor switch (coding style)
Merge branch 'dnstap'
zone-events: reload: Plan DNSSEC signing even if the zone did not
change.
zone-events: Removed or resolved TODOs
tests-extra: change zonefile-sync to 1 day to disable unwanted flush
config: add option system.background-workers
knot.conf manual: add system.background workers
workers: get rid of OpenSSL reachable leaks
rename: free_ddns_q -> free_ddns_queue
zonedb reload synchronization: replace todo with warning
EDNS: Adding empty NSID + print OPTIONs in utils.

- knot_edns_init_from_params() modified to add also empty NSID
  OPTION.
- knot_pkt_add_opt() documented and modified usage not to insert
  emtpy NSID to reply.
- OPTION printing in utils was not implemented.
EDNS: Replaced the explicit owner creation.
zscanner: add check_SCRIPTS to make-compile-only
EDNS: Fixed some unittests.

Mostly wrong test counts.

In the pkt tests, the comparison test is failing, but don't know
why. It's somehow related to the OPT RR, because when I remove its
addition, it doesn't fail anymore. However, I don't know what's
the problem yet.
Merge branch 'zone-events-queue' into opt-refactor
zone-events: Plan NOTIFY after update.