### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

Initiating a multipart S3 upload to LocalStack returns an XML document with a root element CreateMultipartUploadOutput. This causes an error in the ex_aws_s3 library I'm using. We've used the combination of LocalStack + ex_aws_s3 successfully for a few years and the error started occurring a few days ago.

### Expected Behavior

The element should be called InitiateMultipartUploadResult.

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run -p 4566:4566 localstack/localstack

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

    aws --debug --endpoint-url=http://localhost:4566 s3api create-multipart-upload --bucket my-bucket --key 'multipart/01'


### Environment

```markdown
- OS: Ubuntu 20.04.5 LTS
- LocalStack: latest
```


### Anything else?

S3 docs specifying InitiateMultipartUploadResult:
https://docs.aws.amazon.com/AmazonS3/latest/API/API_CreateMultipartUpload.html

Reference in official AWS Java client:
https://github.com/aws/aws-sdk-java/blob/ef22b94750d4c155d74b09012b3be5d9d98bbd33/aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/model/transform/XmlResponsesSaxParser.java#L1865

Where our particular error gets raised in ex_aws_s3:
https://github.com/ex-aws/ex_aws_s3/blob/7e12f2b0578b2620c047d2e44c40a6de8773584a/lib/ex_aws/s3/parsers.ex#L78
erred mime type (based on the serializer's supported mime types and the Accept header)
        mime_type = self._get_mime_type(headers)
        # if the operation has a streaming output, handle the serialization differently
        if operation_model.has_event_stream_output:
            return self._serialize_event_stream(response, operation_model, mime_type)
        serialized_response = self._create_default_roperation_model, mime_type)
        shape = operation_model.output_shape
        # The shape can also be none (for empty responses), but it still needs to be serialized (to add some metadata)
        shape_members = shape.members if shape is not None else None
        self._serialize_r
            response, serialized_response, shape, shape_members, operation_model, mime_type
        )
        serialized_response = self._prepare_additional_traits_in_r
            serialized_response, operation_model
        )
        return serialized_response
    @_handle_exceptions
    def serialize_error_to_r
        self,
        error: ServiceException,
        operation_model: OperationModel,
        headers: Optional[Dict | Headers],
    ) -> HttpResponse:
        """
        Takes an error instance and serializes it to an actual HttpResponse.
        Therefore, this method is used for errors which should be serialized and transmitted to the calling client.
        :param error: to serialize
        :param 
                                service's output / response
        :param headers: the headers of the incoming requ
                        for features like Content-Negotiation 
        :return: HttpResponse which can be sent to the calling client
        :raises: ResponseSerializerError (either a ProtocolSerializerError or an UnknownSerializerError)
        """
        # determine the preferred mime type (based on the serializer's supported mime types and the Accept header)
        mime_type = self._get_mime_type(headers)
        # TODO implement streaming error s