Use model to translate operationInput parameters

[alextwoods]

Example operationInputTest with issue:

"operationName": "BatchGetItem",
                    "operationParams": {
                        "RequestItems": {
                            "arn:aws:dynamodb:us-east-1:333333333333:table/table_name": {
                                "Keys": [
                                    {
                                        "pk": {
                                            "S": "value"
                                        }
                                    }
                                ]
                            }
                        }
                    }

Before:

resp = client.batch_get_item(
          request_items: {:arn_aws_dynamodb_us_east_1_333333333333_table_table_name=>{:keys=>[{:pk=>{:s=>"value"}}]}},
        )

After:

resp = client.batch_get_item(
          request_items: {"arn:aws:dynamodb:us-east-1:333333333333:table/table_name"=>{:keys=>[{"pk"=>{:s=>"value"}}]}},
        )

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