chg: dev: No effective config as text if allow-new-zones is yes

Do not save the text version of the effective configuration when
`allow-new-zones` is enabled, as in that case the object tree can
be printed on demand, reducing unnecessary memory consumption.

Merge branch 'colin/no-effective-config-as-text-allownewzones' into 'main'

See merge request isc-projects/bind9!11242