Bin Optimizer task

[mafrahm]

We need a task to call some kind of bin optimizer, which takes as requirements events or histograms from multiple datasets and configs (defined by the class itself). One should then be able to give this bin optimizer to a variable, which then requires the corresponding task to be run as part of the requirements of CreateHistograms.

In the final task structure, this could look like this.

flowchart TD
    C(CreateHistograms)
    M(MergeHistograms)
    O(OptimizeBinning)
    P(ProduceColumns)

    P --> C --> M 
    P -- multiple datasets, configs --> O
    M -- multiple datasets, configs --> O
    O --> C

Example:
We declared some variable requiring some bin_optimizer

config.add_variable(
   name="my_variable",
   binning="my_bin_optimizer",  # maybe also as a separate field or an aux
)

And now want to create histograms/plots with this variable, e.g.

law run cf.CreateHistograms --version v1 --variable my_variable --dataset tt_sl_powheg

This should trigger the OptimizeBinning task for all the processes required there.
For example, if my_bin_optimizer implements a flat background binning, it should trigger the requirements (e.g. MergeHistograms) for all background processes.