Update models (#2999)

## Motivation and Context
For #2998, I want a clean codegen diff if possible, so splitting out the
models update ahead of time.

## Testing
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## Checklist
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- [ ] 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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