Similar to notify, add code to send and keep track of checkds requests.
On every zone_rekey event, we will check the DS at parental agents
(but we will only actually query parental agents if theree is a DS
scheduled to be published/withdrawn).
On a zone_rekey event, we will first clear the ongoing checkds requests.
Reset the counter, to avoid continuing KSK rollover premature.
This has the risk that if zone_rekey events happen too soon after each
other, there are redundant DS queries to the parental agents. But
if TTLs and the configured durations in the dnssec-policy are sane (as
in not ridiculous short) the chance of this happening is low.
Update: Remove the TLS bits as this is not supported in 9.16
(cherry picked from commit f7872dbd20)
d565dd6190