pdnsutil {add-record,delete-rrset}: Require NAME to be absolute

pdnsutil {add-record,delete-rrset}: Require NAME to be absolute

Note this is an incompatible change because calls like

	pdnsutil --config-dir=configs/auth add-record example.net . NS 1.2.3.4

which added the NS record to the zone's apex before and is an error now.

Note that also "@" isn't interpreted any more as "at the apex".

Adapt the test suite and docs accordingly to use absolute names.

Closes: https://github.com/PowerDNS/pdns/issues/8595