[ntuple] Better control of cluster ordering for parallel writes

[jblomer]

Explain what you would like to see improved and how.

The RNTupleParallelWriter should be extended to allow to fix the logical order of clusters written to disk. This would allow to better align parallel writing with, e.g., lumi blocks. The physical on-disk order of clusters written by the parallel writer will still be arbitrary, but the meta-data can link them to another, logical order.

ROOT version

master

Installation method

n/a

Operating system

n/a

Additional context

No response