Detect duplicate VASP entity registrations

[bbengfort]

Currently, registration is conditioned on the unique common_name field which should be the domain of the TRISA endpoint. We need a better way to distinguish between multiple registrations of the same legal entity.

In the Register() RPC call, there is a TODO that specifies duplicate detection should be done with the entity signature - a hash or checksum of the IVMS101 legal entity. The question is how to produce this hash.

One suggestion is to hash the name identifiers and country field; another is to simply use any "legal name" identifiers in the entity" or to use the government identification field. Whatever choice is made, the signature should be able to uniquely recognize a legal person record across various versions and manipulations (e.g. with multiple addresses, name identifiers, etc).