Add error code to error type map

[adam-fowler]

This PR goes hand in hand with soto-project/soto-core#649

Makes extended error information available via AWSErrorType.context.extendedError if available eg

do
    let updateRequest = try DynamoDB.UpdateItemCodableInput(...)
    _ = try await Self.dynamoDB.updateItem(updateRequest, logger: TestEnvironment.logger)
} catch let error as DynamoDBErrorType where error == .conditionalCheckFailedException {
    if let conditionError = error.context?.extendedError as? DynamoDB.ConditionalCheckFailedException {
        ...
    }
}