feat: add config option to enable path-style URLs for S3 API calls

[tcsavage]

Issue #, if available: aws-controllers-k8s/community#2237

Description of changes:

In order to support some S3-compatible APIs (e.g. LocalStack on a local dev cluster) it may be necessary to force the S3 client to use "path-style" URLs (e.g. http://host/bucket/key).

This PR adds a UsePathStyle config field and --aws-endpoint-use-path-style CLI flag to force path-style S3 URLs. This will be used by the S3 controller to configure the service client.

Associated PRs:

• code-generator#684 adds a necessary hook to allow configuring the service client based on this config option.
• s3-controller#214 uses the hook created in the code-generator PR.

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

[ack-prow]

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This pull-request has been approved by: tcsavage
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[ack-prow]

Hi @tcsavage. Thanks for your PR.

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