…ection

As discussed in aws/aws-sdk-go-v2#3003 and
aws/aws-sdk-go-v2#2960,
`github.com/aws/aws-sdk-go-v2/service/s3` v1.73.0 changed the AWS SDK
default object integrity behavior. Third-party S3 providers, such as
Linode, may fail with `XAmzContentSHA256Mismatch` error as a result.

A workaround is to set the `AWS_REQUEST_CHECKSUM_CALCULATION`
and `AWS_RESPONSE_CHECKSUM_VALIDATION` to `when_required`.

However, these environment variables do not affect multipart uploads
that used the SDK's `manager.Uploader` implementation
(aws/aws-sdk-go-v2#3007). Multipart uploads
fail with a 400 Bad Request due to the inclusion of
`X-Amz-Sdk-Checksum-Algorithm: CRC32` HTTP headers. With
aws/aws-sdk-go-v2#3151, the default integrity
protection can be explicitly configured for `manager.Uploader`.

To ensure backwards compatibility with third-party S3 providers, this
commit adds support for two query parameters:

* `request_checksum_calculation` - `when_supported`, `when_required`
* `response_checksum_calculation` - `when_supported`, `when_required`

For example, on Linode, the defaults don't work:

```
% cat main.go | ./gocdk-blob upload "s3://smybucket?endpoint=https://us-sea-1.linodeobjects.com&region=us-sea-1" main.go
gocdk-blob: closing the writer: blob (key "main.go") (code=Unknown): operation error S3: PutObject, https response error StatusCode: 400, RequestID: <redacted>, HostID: <redacted>, api error XAmzContentSHA256Mismatch: UnknownError
```

Using `request_checksum_calculation=when_required` works:

```
% cat main.go | ./gocdk-blob upload "s3://smybucket?endpoint=https://us-sea-1.linodeobjects.com&region=us-sea-1&request_checksum_calculation=when_required" main.go
%
```

This test was repeated with a larger to validate multipart uploads work.