Document additional backend configuration

[jyu00]

What is the expected enhancement?

Today IBMBackend.configuration() returns a BackendConfiguration class that lives in Qiskit. Since Qiskit is provider agnostic, this class doesn't have the additional fields that are returned by IBM backends. Some examples include backend.configuration().supported_features (which tells you whether dynamic circuits are supported), and parallel_compilation. Users would then have to learn about their existence through word of mouth instead of simply searching the API. These fields are also not documented in the schema.

Acceptance criteria

A user can find all backend configurations in the API Reference.