Add device component experiment metadata

[coruscating]

Summary

This PR adds a device_components field to the experiment metadata that is a list of qubits used in the experiment by default. Experiments that use custom components need to override this metadata field (just ResonatorSpectroscopy so far). It also exposes device components in the documentation and updates the custom experiment tutorial. #1163 depends on this PR to add the metadata so that non-qubit components can be correctly identified for figure names.

[nkanazawa1989]

I think this is a nice update. However, base experiment class returns just an index list of physical qubits, rather than list of device component Qubit. To unify metadata, I think we should also add "device_component" to the base experiment with Qubit instance.

[coruscating]

That's a good suggestion @nkanazawa1989, I've made device_components populated by Qubits by default in BaseExperiment. I also exposed index in DeviceComponent subclasses as per @wshanks's feedback.

[wshanks]

Looks good to me! I wonder if we want to make it easier to define a custom device component (maybe a generic component that just serializes to a string without needing a class?), but we don't have to worry about that here.