fix: usr: Preserve cache across reconfig when using attach-cache

When the `attach-cache` option is used in the `options` block with an arbitrary name, it causes all views to use the same cache. Previously, this configuration caused the cache to be deleted and a new cache created every time the server was reconfigured. This has been fixed.

Closes #5061

Merge branch '5061-attach-cache-fix' into 'main'

See merge request isc-projects/bind9!9787