Support all RDAP JSON Values from the IANA registry

[Melebius]

Expected behavior

All values listed on the page https://www.iana.org/assignments/rdap-json-values/rdap-json-values.xhtml should be accepted for the corresponding RDAP fields.

Actual behavior

Only the values defined in RFC 7483 seem to be accepted currently, according to my rdap-conformance output:

...
entity.standard,http://rdap:8000/entity/LISTER,failure,content,invalid: last update of RDAP database,"events":0:"eventAction",rfc7483,10.2.3
...

Context

The affected value last update of RDAP database is not mentioned in RFC 7483, but is present in rdap-json-values.xhtml. Section 10.2 of RFC 7483 (or 9083) says:

IANA has created a category in the protocol registries labeled "Registration Data Access Protocol (RDAP)", and within that category, IANA has established a URL-referenceable, stand-alone registry labeled "RDAP JSON Values".
(...)
The following sections provide initial registrations into this registry.

So please accept the values added later (by different registrants), in addition to those defined directly in RFC 7483.