Internal reference: D166315367

In FIPS enabled environments, the MD5 algorithm is not available for use in crypto module.
However by default the S3 client is using an MD5 checksum for content integrity checking.
This causes any S3 upload operation to fail with a cryptography error.

We are disabling the S3 content checksums, and are re-enabling the regular SigV4 body signing.
SigV4 uses SHA256 for their content checksum. This configuration matches the default behavior
of the AWS SDKv3 and is a safe choice for all users.

For non-FIPS users, we have verified functionality via cli-integ-tests.
For FIPS users, we have manually verified `cdk deploy` is now working in a FIPS enabled environment.
We have also verified the configuration with the affected customer.

- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

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