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

[phantumcode]

• PR title and description conform to Pull Request guidelines.

Issue #, if available:
#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: aws-amplify/docs#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
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• 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.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 23.33333% with 23 lines in your changes missing coverage. Please review.

Project coverage is 44.02%. Comparing base (0f61cc8) to head (05f1e84).
Report is 35 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2848      +/-   ##
==========================================
+ Coverage   43.00%   44.02%   +1.01%     
==========================================
  Files         905      925      +20     
  Lines       29179    30293    +1114     
  Branches     4153     4305     +152     
==========================================
+ Hits        12549    13335     +786     
- Misses      15271    15531     +260     
- Partials     1359     1427      +68     

[tylerjroach]

Nice work, a few suggested changes.