S3 Multipart upload/download update

[jterapin]

Objectives:

• Ensure that temp file is deleted when multipart download fails (and do not overrwrite if a file exists)
• Added various validation checks

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

1. To make sure we include your contribution in the release notes, please make sure to add description entry for your changes in the "unreleased changes" section of the CHANGELOG.md file (at corresponding gem). For the description entry, please make sure it lives in one line and starts with Feature or Issue in the correct format.

2. For generated code changes, please checkout below instructions first:
   https://github.com/aws/aws-sdk-ruby/blob/version-3/CONTRIBUTING.md

Thank you for your contribution!

[github-actions]

Detected 1 possible performance regressions:

• aws-sdk-s3.get_object_small_ms - z-score regression: 10.43 -> 15.13. Z-score: 20.03

[mullermp]

Seems fine in general. Be sure to run integration tests and also do manual tests.

[mullermp]

Looks good, be sure to run integ tests and some manual testing. Even better if you want to add a cucumber test.