chg: dev: parse user configuration before exclusive mode

chg: dev: parse user configuration before exclusive mode

Previously, `named.conf` was parsed while the server was in exclusive (i.e., single-threaded) mode and unable to answer queries. This could cause an unnecessary delay in query processing when the file was large. We now delay entry into exclusive mode until after the configuration has been parsed, but before it is applied.

Merge branch 'colin/configparse-before-exclusive' into 'main'

See merge request isc-projects/bind9!10418