Make the AWS specific retry policy inheritable

[aajtodd]

Describe the feature

Customers often want/need to retry specific errors. They can do this now by re-using AwsDefaultRetryPolicy but because it's an object and not an open ended class to be extended from it limits how customers can implement custom policies (specifically they have to compose it into a new policy and delegate down to the default if needed).

e.g.

class CustomRetryPolicy : RetryPolicy<Any?> {
    override fun evaluate(result: Result<Any?>): RetryDirective {
        return when(result.exceptionOrNull()) {
            is IOException -> RetryDirective.RetryError(RetryErrorType.Transient)
            else -> AwsDefaultRetryPolicy.evaluate(result)
        }
    }
}

Is your Feature Request related to a problem?

See smithy-lang/smithy-kotlin#962 for one example.

Proposed Solution

refactor AwsDefaultRetryPolicy to look like the StandardRetryPolicy.

e.g.

public open class AwsRetryPolicy: StandardRetryPolicy() {
      companion object {
           val Default: AwsRetryPolicy = AwsRetryPolicy()
      }
      ...
}

---

Customer code becomes:

class CustomRetryPolicy: AwsRetryPolicy() {
    override fun evaluateSpecificExceptions(ex: Throwable): RetryDirective? = when(ex){
        is IOException -> RetryDirective.RetryError(RetryErrorType.Transient)
        else -> super.evaluateSpecificExceptions(ex)
    }
}

Describe alternative solutions or features you've considered

No response

Acknowledge

• I may be able to implement this feature request

AWS Kotlin SDK version used

0.32.x+

Platform (JVM/JS/Native)

N/A

Operating System and version

N/A

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