Enable serialization of Optimizers

[Cryoris]

What is the expected enhancement?

Enable serialization and de-serialization of the Optimizers such that they can be sent to Qiskit Runtime as algorithm settings. This is easily done by adding to_dict and from_dict methods and agree on a common structure, such as

{'name': 'SPSA',  # required key
 'maxiter': 100,
 # other settings
}

It's probably best to wait after #6319 is merged and then add it to the SciPyMinimizer base class.

[Cryoris]

This will be closed by #6545 but for serialization for Qiskit Runtime we'll have to add encoding and decoding logic in the provider.