Run Stas' bandwidth testing code on LUMI

[dirkgr]

Stas' code is here: https://github.com/stas00/toolbox/blob/master/pytorch/all_reduce_bench.py

We should run this on a single node, and multiple nodes.

[dirkgr]

I gave this "medium" difficulty because you have to figure out how to run in LUMI for this.

[dumitrac]

Marking the items prior to Feb 29th as "closed".