### 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
of ResponseSerializerError.
    :param func: to wrap in order to add the exception handling
    :return: wrapped function
    """
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        try:
            return func(*args, **kwargs)
        except ResponseSerializerError:
            raise
        except Exception as e:
            raise UnknownSerializerError(
                "An unknown error occurred when trying to serialize the response."
            ) from e
    return wrapper
class ResponseSerializer(abc.ABC):
    """
    The response serializer is responsible for the serialization of a service implementation's result to an actual
    HTTP response (which will be sent to the calling client).
    It is the base class of all serializers and therefore contains the basic logic which is used among all of them.
    """
    DEFAULT_ENCODING = "utf-8"
    # The default timestamp format is ISO8601, but this can be overwritten by subclasses.
    TIMESTAMP_FORMAT = "iso8601"
    # Event streaming binary data type mapping for type "string"
    AWS_BINARY_DATA_TYPE_STRING = 7
    # Defines the supported mime types of the specific serializer. Sorted by priority (preferred / default first).
    # Needs to be specified by subclasses.
    SUPPORTED_MIME_TYPES: List[str] = []
    @_handle_exceptions
    def serialize_to_r
        self, response: dict, operation_model: OperationModel, headers: Optional[Dict | Headers]
    ) -> HttpResponse:
        """
        Takes a response dict and serializes it to an actual HttpResponse.
        :param response: 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 pref