[request]: sts::model::Credentials should implement AsyncProvideCredentials

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**Tell us about your request**
All `Credentials` models should implement `AsyncProvideCredentials` or `ProvideCredentials` to easily create new connections using temporary credentials.

For example `sts::model::Credentials` does not while `aws_auth::Credentials` for example implements `ProvideCredentials`. Anyway there should be only one `Credentials` i guess

**Attachments**
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Start by comparing sts::model::Credentials with aws_auth::Credentials and inspect the AsyncProvideCredentials and ProvideCredentials traits they are expected to implement. Clarify whether the request applies to all Credentials models or specifically STS, then verify the selected implementation supports creating connections with temporary credentials.

Written by the indexing model from the issue text.