Update whitepaper to reflect changes in tbdex-protocol repo

[jiyoonie9]

The tbdex-protocol repo has seen a few set of changes in the last couple months. It would be good to keep the whitepaper up to date with some of the major changes.

Some notable changes to include in the next whitepaper version:

• Concept of tbDEX Resource vs tbDEX Messages
• Introduction of metadata such as from, to, threadId, parentId