Improved docs for EnsembleProblem

[baggepinnen]

Looking into the advanced features of the EnsembleProblem, I find it hard to understand what the u, data and I arguments for the reduction function are.
https://docs.sciml.ai/DiffEqDocs/latest/features/ensemble/#Performing-an-Ensemble-Simulation
It would also be nice if slightly more informative docstrings were available

help?> EnsembleProblem
search: EnsembleProblem

  struct EnsembleProblem{T, T2, T3, T4, T5} <: SciMLBase.AbstractEnsembleProblem

[Zf98ai]

Hi! I'd like to take on this issue.

I'll work on improving the documentation for the 'reduction' function in ensemble simulations and enhance the docstring of 'EnsembleProblem' for clarity. Planning to add clearer explanations for 'u', 'data', and 'I', and improve the docstring content with examples.

@SciML Let me know if this sounds good or if there's anything I should be aware of before proceeding.

[ChrisRackauckas]

Those are definitely needed.