Conversion interface to/from `qiskit-fermions` objects.

### Motivation

`qiskit-fermions` provides APIs to express fermionic problems: https://qiskit.github.io/qiskit-fermions/dev/index.html

### Proposed feature

An interface to translate to our internal representation of such Fermionic objects.

### Proposed API or usage example (optional)

_No response_

### Additional context

_No response_