Make Signed documents library have a basic deserializer

[stevenj]

Summary

Create a simple deserializer api for the signed docs library

Description

• 1. Change all ULID's to UUIDv7 in spec. And clarify UUID is UUIDv4 in spec.
• 2. Adjust the signed document builder to use UUIDv7.
• 3. Create an API to deserialize the signed document for use by cat-gateway.