Implement option fo stochastic forcing

[JanJereczek]

Motivation

The forcing of any ice sheet is subject to noise and implementing the possibility of providing a stochastic forcing would allow:

1. Studying noise-induced transitions
2. Running analyses of transitions with TransitionsInTimeseries.jl

Difficulties

The main difficulty might be to have a realistic coherence of the noise in time and space.

Resources

Dani already has scripts to generate noise as in Christian et al. (2021)

[alex-robinson]

Note there is already some functionality to add white noise to forcing in the hyster module. This has slowly become an all-purpose time series forcing module as opposed to just one for hysteresis experiments. The module should probably be renamed and refactored, but this would be a natural place to add more types of noise for now.