Feature request: support exclusive put mode

[martindurant]

This is the "conditional upload" feature, supported by AWS and others for atomic writes, equivalent to "xb" locally. The mode is important, for example, to icechunk, which uses the store atomic operation to ensure there is no race in setting the latest version of a dataset.

cf fsspec/filesystem_spec#1693

[martindurant]

On closer reading, I suppose "create" does exactly this - apologies.

[kylebarron]

I think so, yes. We should test that it is indeed working on s3

[kylebarron]

See also apache/arrow-rs#6285

[martindurant]

We should test that it is indeed working on s3

I bet it doesn't on moto... I hear that minio have had it a while, though.

[kylebarron]

I mean we should manually test this on an actual S3 bucket.