JSON or ConceptDocument should implement Serialize

[dmitrii-ubskii]

Problem to Solve

axum, e.g., allows any struct that implements Serialize to be a part of its own Json structure which can handle serialization and content headers in the server response. With Serialize we would be able to pipe the fetch output directly into the response.

Current Workaround

Either constructing the JSON manually, or reparsing the JSON as serde_json::RawValue.

Proposed Solution

Implement Serialize for JSON.

Additional Information

[farost]

We should probably reimplement something very similar to the HTTP endpoint's message structures from the server. It will include the requested feature. Agreed.