fix: test: Combine rollover system tests

`rollover` and the dozen or so related system tests (`rollover_algo_csk`, `rollover_algo_ksk_zsk`, etc) share most of their files in common, and can be simplified into a single directory structure.

Merge branch 'each-declutter-rollover-tests' into 'main'

See merge request isc-projects/bind9!12523