Switch to aws-sdk-go-v2

[mjlshen]

This PR switches the codebase from aws-sdk-go to aws-sdk-go-v2 due to aws-sdk-go going EoL next year https://aws.amazon.com/blogs/developer/announcing-end-of-support-for-aws-sdk-for-go-v1-on-july-31-2025/

For the most part, it is faithful to the original code, some differences to highlight:

• The httputil package was removed from this codebase - it was providing an implementation of a client-side rate limiter that is now built-in functionality in aws-sdk-go-v2.
• The CredentialsChainVerboseErrors option was removed in aws-sdk-go-v2 What happened to CredentialsChainVerboseErrors? aws/aws-sdk-go-v2#98

Fixes #117

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[k8s-ci-robot]

@mjlshen: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-aws-encryption-provider-verify	0d0cbec	link	true	/test pull-aws-encryption-provider-verify

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[mjlshen]

I tried to keep this code as similar to the original version as possible, but there are two considerations I ran into that I'm happy to implement if reviewers think they're better

1. It may make more sense to use errors.As to filter errors instead of switching on the error code https://aws.github.io/aws-sdk-go-v2/docs/handling-errors/#api-error-responses
2. The smithy.APIError type has an ErrorFault method that classifies certain errors as client/server/unknown faults https://pkg.go.dev/github.com/aws/smithy-go#ErrorFault. This could be used instead of maintaining our own list of client-fault error codes.