Anon bucket

[valeriupredoi]

Description

Closes #291

Changes in Client to emit data for Anon bucket. @maxstack it currently doesn't work from Reductionist's end, Reductionist throws a 401, could you have a look pls mate 🍺 - the test to look at is tests/test_real_s3.py::test_anon_s3 see the failed test here https://github.com/NCAS-CMS/PyActiveStorage/actions/runs/23255142731/job/67607820849?pr=314

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