Retry additional classes of H2 errors (#2971)

Draft pull request pending merge of #2970 
## Motivation and Context
- https://github.com/awslabs/aws-sdk-rust/issues/738
- https://github.com/awslabs/aws-sdk-rust/issues/858
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## Description
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This PR adds two additional classes of retries tested:
1. GO_AWAY: https://github.com/awslabs/aws-sdk-rust/issues/738
2. REFUSED_STREAM: https://github.com/awslabs/aws-sdk-rust/issues/858

I tested 1 by using the example helpfully provided. The fix for 2 is
untested and difficult to reproduce but since my fix for 1 worked, I'm
confident that we're detecting the correct error class here.

## Testing
I used the example provided by the customer and validated the H2 GO_AWAY
fix.

## Checklist
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rather than leaving it unchecked -->
- [ ] I have updated `CHANGELOG.next.toml` if I made changes to the
smithy-rs codegen or runtime crates
- [ ] I have updated `CHANGELOG.next.toml` if I made changes to the AWS
SDK, generated SDK code, or SDK runtime crates

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