[9.20] fix: usr: Resolve the spurious drops in performance due GLUE cache

For performance reasons, the returned GLUE records are cached on the first use.  The current implementation could randomly cause a performance drop and increased memory use.  This has been fixed.

Closes #5064

Backport of MR !9831

Merge branch 'backport-5064-rewrite-glue-cache-in-qpzone-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!9918