chg: dev: Create list of dirty headers that needs cleaning

Instead of just flagging the qpcache node to be dirty, add the headers
to be cleaned to the dirty list and when cleaning the node, only walk
through the dirty node, not all the headers in the node.

Merge branch 'ondrej/optimize-qpcache-dirty-cleaning' into 'main'

See merge request isc-projects/bind9!11164