[S2S] Determine the correct document structure for Server-to-Server and Canonical VCI

The initial draft is created as a parallel document without direct dependencies between the two. Before S2S Implementors Draft 1, we should determine the correct document structure to have. We expect there to be many shared structures and features between the two as they are functionally performing the same operation (issuing credentials to a Wallet)

Options are:

1. Two documents that define separate but equivalent structures
2. Three documents, Canonical VCI, S2S VCI and VCI Primitives/Building Blocks
3. Two documents: Canoncial VCI refactored to allow reference to , and S2S VCI referencing building blocks
4. One document structured so the primitives are the same and then S2S and Canonical describe how they are used in their two contexts

See #754 for a list of the shared features between the two approaches.

I would prefer not 1, leaning towards 3 but don't feel strongly about 2-4.

Start by reading issue #754 for the listed shared features between Server-to-Server and Canonical VCI. Compare the four proposed document structures and assess how each supports shared primitives and context-specific usage. Done means agreeing on the document structure before S2S Implementors Draft 1.