[9.20] new: usr: Added WALLET type

Add the new record type WALLET (262).  This provides a mapping from a domain name to a cryptographic currency wallet.  Multiple mappings can exist if multiple records exist.

Closes #4947

Backport of MR !9521

Merge branch 'backport-4947-add-wallet-type-to-named-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!9554