test/e2e/s3: add tests for S3 server 5xx

[alxndrsn]

TODO

Given obscurity of error handling, and opportunity for future improvement, make these tests document existing behaviour without considering modification of the lib/ code.

Ref minio/minio-js#1475

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Ref getodk/central#1862

Closes getodk/central#

What has been done to verify that this works as intended?

Why is this the best possible solution? Were any other approaches considered?

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Does this change require updates to the API documentation? If so, please update docs/api.yaml as part of this PR.

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