Dask for template histogram construction

[alexander-held]

With dask-awkward and integration with hist, it seems conceptually possible to make the template histogram creation fully Dask-driven. This could result in two significant improvements:

• parallelization of template histogram construction,
• optimization of data processing, e.g. avoiding duplicate data reading when filling lots of histograms that only differ by a weight.

The latter requires dask-awkward and dask-histogram and needs to build the full task graph before calling compute. This is a much bigger change than providing an interface that allows distribution of template construction (which acts as a black box function) via e.g. Dask.

[alexander-held]

An intermediate solution that might also help is the possibility to run histogram production on a subset of all templates via some filter, allowing to parallelize manually by calling the same function with different filters.