feat(storage): add object existence validation option to get presigned url

[phantumcode]

• [x] PR title and description conform to Pull Request guidelines.

Issue #, if available: https://github.com/aws-amplify/amplify-android/issues/2404

Description of changes: Update Storage getURL options to have a boolean flag to check for object existence. This provides feature parity with Amplify Swift

Doc PR: https://github.com/aws-amplify/docs/pull/7736

How did you test these changes?

• Manually tested getURL with new option enabled/disabled with and without object
• Added unit tests

Documentation update required?

• [ ] No
• [x] Yes (Please include a PR link for the documentation update)

General Checklist

• [x] Added Unit Tests
• [x] Added Integration Tests
• [x] Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)

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