Add AWS SDK clients for CFN Custom Resource support

[flostadler]

This change adds the necessary AWS SDK clients (S3 and Lambda) for supporting CFN Custom Resources in aws-native.

Relates to https://github.com/pulumi/pulumi-cdk/issues/109

[flostadler]

This change is part of the following stack:

• 1805 ◀

  • 1808

    • 1806

      • 1807

_{Change managed by git-spice.}

[github-actions[bot]]

Does the PR have any schema changes?

Looking good! No breaking changes found. No new resources/functions.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 70.14218% with 63 lines in your changes missing coverage. Please review.

Project coverage is 46.30%. Comparing base (91e1b65) to head (6575dfa). Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
provider/pkg/client/mock_s3.go	65.38%	26 Missing and 1 partial :warning:
provider/pkg/client/mock_lambda.go	64.58%	16 Missing and 1 partial :warning:
provider/pkg/client/lambda.go	75.55%	10 Missing and 1 partial :warning:
provider/pkg/client/s3.go	80.00%	7 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1805 +/- ## ========================================== + Coverage 45.44% 46.30% +0.85% ========================================== Files 38 42 +4 Lines 5886 6097 +211 ========================================== + Hits 2675 2823 +148 - Misses 2988 3047 +59 - Partials 223 227 +4 ```

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