object_store(aws): EntityTooSmall error on multi-part upload

[wjones127]

Describe the bug

Our multi-part upload pieces are too small for the AWS API's liking. Currently, it is using 5,000,000 byte parts, but minimum is either 5 MB or 5 MiB (not sure).

Example error:

thread 'aws::tests::s3_test' panicked at 'called `Result::unwrap()` on an `Err` value: Custom { kind: Other, error: Generic { store: "S3", source: CompleteMultipartRequest { source: Error { retries: 0, message: "<Error><Code>EntityTooSmall</Code><Message>Your proposed upload is smaller than the minimum allowed size</Message><ProposedSize>5123000</ProposedSize><MinSizeAllowed>5242880</MinSizeAllowed><PartNumber>1</PartNumber><ETag>dac58c3bc3316365210fc576472b529a</ETag><RequestId>NAFF7PP64BMSNE2N</RequestId><HostId>r7Fu4+ISmVItLuVku0lD+SZFlQmQFskejoOBwSru7JzJ/KFNQ7/Ae/nyszZGtNhWAaMqrmLXuqk=</HostId></Error>", source: Some(reqwest::Error { kind: Status(400), url: Url { scheme: "https", cannot_be_a_base: false, username: "", password: None, host: Some(Domain("s3.us-west-2.amazonaws.com")), port: None, path: "/wjones127-test-object-store/test_dir/test_upload_file.txt", query: Some("uploadId=mQw8lAvgQI8SFAosOZgucoX80ZC0yf6j6lBctI_CoiM09jg5TVGOHnaOy7QVUARnH2FrxjPOMc8g892B4qK_7CWYhHRU9wzcGTzBLvGKAYI-"), fragment: None } }) } } } }', object_store/src/lib.rs:778:33

To Reproduce

Expected behavior

Additional context

Reported in delta-rs: delta-io/delta-rs#890 (comment)