Add benchmarks reading from cloud object storage?

[JackKelly]

Thank you so much for all your work on zarrs, zarr_benchmarks, etc.!

(I feel bad because I'm the guy who started - and then abandoned - the zarr-developers/zarr-benchmark repo. So thank you for doing such a great job with this repo! I appreciate that benchmarking is surprisingly hard!)

I'd be super-curious to see how these different Zarr implementations perform when reading from cloud object storage.