### 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
s3_ReducedRedundancyLostObject = "s3:ReducedRedundancyLostObject"
    s3_ObjectCreated_ = "s3:ObjectCreated:*"
    s3_ObjectCreated_Put = "s3:ObjectCreated:Put"
    s3_ObjectCreated_Post = "s3:ObjectCreated:Post"
    s3_ObjectCreated_Copy = "s3:ObjectCreated:Copy"
    s3_ObjectCreated_CompleteMultipartUpload = "s3:ObjectCreated:CompleteMultipartUpload"
    s3_ObjectRemoved_ = "s3:ObjectRemoved:*"
    s3_ObjectRemoved_Delete = "s3:ObjectRemoved:Delete"
    s3_ObjectRemoved_DeleteMarkerCreated = "s3:ObjectRemoved:DeleteMarkerCreated"
    s3_ObjectRestore_ = "s3:ObjectRestore:*"
    s3_ObjectRestore_Post = "s3:ObjectRestore:Post"
    s3_ObjectRestore_Completed = "s3:ObjectRestore:Completed"
    s3_Replication_ = "s3:Replication:*"
    s3_Replication_OperationFailedReplication = "s3:Replication:OperationFailedReplication"
    s3_Replication_OperationNotTracked = "s3:Replication:OperationNotTracked"
    s3_Replication_OperationMissedThreshold = "s3:Replication:OperationMissedThreshold"
    s3_Replication_OperationReplicatedAfterThreshold = (
        "s3:Replication:OperationReplicatedAfterThreshold"
    )
    s3_ObjectRestore_Delete = "s3:ObjectRestore:Delete"
    s3_LifecycleTransition = "s3:LifecycleTransition"
    s3_IntelligentTiering = "s3:IntelligentTiering"
    s3_ObjectAcl_Put = "s3:ObjectAcl:Put"
    s3_LifecycleExpiration_ = "s3:LifecycleExpiration:*"
    s3_LifecycleExpiration_Delete = "s3:LifecycleExpiration:Delete"
    s3_LifecycleExpiration_DeleteMarkerCreated = "s3:LifecycleExpiration:DeleteMarkerCreated"
    s3_ObjectTagging_ = "s3:ObjectTagging:*"
    s3_ObjectTagging_Put = "s3:ObjectTagging:Put"
    s3_ObjectTagging_Delete = "s3:ObjectTagging:Delete"
class ExistingObjectReplicationStatus(str):