Add `sdk_ua_app_id` in addition to sdk-ua-app-id in profile file support (#2724)

## Motivation and Context
The field name is being changed, but we need to maintain support for
customers already using this feature

## Description
<!--- Describe your changes in detail -->

## Testing
- existing tests

## Checklist
<!--- If a checkbox below is not applicable, then please DELETE it
rather than leaving it unchecked -->
- [x] I have updated `CHANGELOG.next.toml` if I made changes to the
smithy-rs codegen or runtime crates
- [x] 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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