Ensure identity resolver is set when a credentials provider is given only at...

Ensure identity resolver is set when a credentials provider is given only at operation level (#3156)

## Motivation and Context
Fixes https://github.com/awslabs/aws-sdk-rust/issues/901

## Description
This PR is a rework of https://github.com/awslabs/smithy-rs/pull/3021
whose fix was inadvertently discarded during
https://github.com/awslabs/smithy-rs/pull/3077. The way we fix the issue
is slightly different. In this PR, we add an identity resolver to
runtime components within `set_credentials_provider`, instead of using
`ServiceConfig.OperationConfigOverride`.

## Testing
Added a Kotlin integration test to `CredentialProviderConfigTest.kt`
based on the customer reported issue.

## 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 AWS
SDK, generated SDK code, or SDK runtime crates

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