[9.20] fix: usr: Make catalog zone names and member zones' entry names case-insensitive

Previously, the catalog zone names and their member zones' entry
names were unintentionally case-sensitive. This has been fixed.

Closes #5693

Backport of MR !11410

Merge branch 'backport-5693-catz-case-sensitivity-fix-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!11450