Add support for ODE parameters

[robin-janssen]

There are many cases where in addition to the initial conditions of the ODE, external parameters like density, radiation flux or temperature could influence trajectories, where identical initial conditions evolve differently based on these external parameters. While they could be treated as species that remain constant over the course of the time-evolution, this does not capture the nature of these quantities and their interaction with the time-evolution of the chemical abundances.

We need the option to add parameters to the dataset. These will be assumed to be constant for any sample over the course of the time-evolution.
This must be implemented into each surrogate, the create_dataloader method as well as into the create_dataset function.