Update schema and add tests to verify they are kept up-to-date

[Hofer-Julian]

We have a Pydantic model for our JSON-RPC communication in here, which can be exported as JSON schema.

However, we don't keep it up-to-date.
We should update it, and then add tests to make sure they keep being up-to-date

[baszalmstra]

Maybe we can use schemars to automate that!