In addition to gather how many times signatures are created per
key in a zone, also count how many of those signature creations are
because of DNSSEC maintenance. These maintenance counters are
incremented if a signature is refreshed (but the RRset did not
changed), when the DNSKEY RRset is changed, and when that leads
to additional RRset / RRSIG updates (for example SOA, NSEC).
This adds tests to the statschannel system test for testing if
the dnskey sign operation counters are incremented correctly.
It tests three cases:
1. A zone maintenance event where all the signatures that are about
to expire are resigned.
2. A dynamic update event where the new RR and other relevant records
(SOA, NSEC) are resigned.
3. Adding a standby key, that means the DNSKEY and SOA RRset are
resigned.
