Default retry policy always retries client exceptions

[aajtodd]

Describe the bug

The StandardRetryPolicy always evaluates ClientException (and sub classes) as retryable

Expected Behavior

Client exceptions are in general probably not retryable since they all stem from the runtime. The errors usually represent some form of configuration error, serde issue, etc. The policy should be updated to at the very least check the isRetryable metadata (which is present on SdkBaseException) and defaults to false. This would allow for client exceptions to be retried if they explicitly opt-in.

[aajtodd]

This is currently affecting credential providers that have their own retry policy or operations that use credential providers that throw (e.g.) CredentialsProviderException. I hit this working on the ECS provider which has it's own retry policy. The operation that uses the provider will attempt to retry the CredentialsProviderException when it should not (the provider has already determined the error isn't retryable so further attempts all yield the same failure).