move import export case to PSB

[jd-lara]

This function is currently defined in PSI

    function _make_5_bus_with_import_export()
        sys = build_system(PSITestSystems, "c_sys5_uc")

        source = Source(;
            name = "source",
            available = true,
            bus = get_component(ACBus, sys, "nodeC"),
            active_power = 0.0,
            reactive_power = 0.0,
            active_power_limits = (min = -2.0, max = 2.0),
            reactive_power_limits = (min = -2.0, max = 2.0),
            R_th = 0.01,
            X_th = 0.02,
            internal_voltage = 1.0,
            internal_angle = 0.0,
            base_power = 100.0,
        )

        import_curve = make_import_curve(
            [0.0, 100.0, 105.0, 120.0, 200.0],
            [5.0, 10.0, 20.0, 40.0],
        )

        export_curve = make_export_curve(
            [0.0, 100.0, 105.0, 120.0, 200.0],
            [12.0, 8.0, 4.0, 0.0],
        )

        ie_cost = ImportExportCost(;
            import_offer_curves = import_curve,
            export_offer_curves = export_curve,
            ancillary_service_offers = Vector{Service}(),
            energy_import_weekly_limit = 1e6,
            energy_export_weekly_limit = 1e6,
        )

        set_operation_cost!(source, ie_cost)
        add_component!(sys, source)
        return sys
    end