Emulate discontinued IBMQ devices

[vanyae-cqc]

It would be nice to be able to build an Aer NoiseModel from the BackendInfo for an IBMQ device. This would enable the emulation of discontinued IBMQ devices for which we have BackendInfos saved.

Something like:

# An old BackendInfo that we have saved somewhere
old_backend_info: BackendInfo

noise_model: NoiseModel = build_noise_model_from_backend_info(old_backend_info)

# Construct AerBackend based on noise model:
emulator_backend = AerBackend(noise_model=self._noise_model)

[vanyae-cqc]

I will take a look at this for now, and submit a PR if I make any decent progress