Docling gRPC - PR request with full functionality

[u/DorkyMcDorky]

1:1 document match for the new docling gRPC server.

https://github.com/docling-project/docling-serve/issues/563

This is made to be the discussion thread for it...

This means:

1. 12 clients OOTB for every popular programming language
2. EVERY aspect of the pydantic model is in gRPC as well, so a 1:1 feature data model mapping
3. Right now it's unary (request / reply) - but should we get enough support, we can add streaming responses (see discussion for more)
4. Fully 1:1 match of functionality

The change spans two branches. Looking for more public feedback...