### 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
self,
        context: RequestContext,
        request: ListMultipartUploadsRequest,
    ) -> ListMultipartUploadsResult:
        
        
        
        bucket = request["Bucket"]
        moto_backend = get_moto_s3_backend(context)
        
        get_bucket_from_moto(moto_backend=moto_backend, bucket=bucket)
        multiparts = list(moto_backend.get_all_multiparts(bucket).values())
        if (prefix := request.get("Prefix")) is not None:
            multiparts = [upload for upload in multiparts if upload.key_name.startswith(prefix)]
        
        uploads = [
            MultipartUpload(
                Key=upload.key_name,
                UploadId=upload.id,
                Initiator={
                    "ID": f"arn:aws:iam::{context.account_id}:user/user1-11111a31-17b5-4fb7-9df5-b111111f13de",
                    "DisplayName": "user1-11111a31-17b5-4fb7-9df5-b111111f13de",
                },
                Owner={
                    "ID": "75aa57f09aa0c8caeab4f8c24e99d10f8e7faeebf76c078efc7c6caea54ba06a",
                    "DisplayName": "webfile",
                },
                StorageClass=StorageClass.STANDARD,  
                Initiated=datetime.datetime.now(),  
            )