chore(util): use custom MD5 checksum instead of native for FIPS environments

[lukiano]

Logic copied from aws-sdk-js-v3

Let me know your thoughts on this. the browserMd5 file also has a similar logic.

The checksum is used for integrity checks, at least in SQS and S3. Because this isn't about ensuring the data hasn't been tampered with, it should be fine in a FIPS environment. Besides, the V3 of the aws-sdk does the same.

Checklist

• npm run test passes
• changelog is added, npm run add-change

[nguyenpc]

Should this be reviewed and merged? The S3 SSE-C approach won't work in FIPS mode without this.

[kuhe]

For now, please overwrite the AWS.util function in question at runtime with your custom MD5 implementation if you need it in your environment.