### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

When you publish a message to SNS without a *body* (e.g. only attributes) it succeeds.

### Expected Behavior

Trying to publish a message without a *body* should fail (at least it does when trying to do this in AWS)

### How are you starting LocalStack?

Custom (please describe below)

### Steps To Reproduce

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

using Java testcontainers...

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

```bash
#!/bin/sh
 
queue_arn=$(awslocal sqs create-queue --queue-name $QUEUE_NAME --output text)
echo "Queue ARN: $queue_arn"

topic_arn=$(awslocal sns create-topic --name $TOPIC_NAME --output text)
echo "Topic ARN: $topic_arn"

subscription_arn=$(awslocal sns subscribe \
    --attributes RawMessageDelivery=true \
    --topic-arn "$topic_arn" \
    --protocol sqs \
    --notification-endpoint "$queue_arn" \
    --output text)
echo "Subscription ARN: $subscription_arn" 
```


### Environment

```markdown
- OS: OSX 11.5.2
- LocalStack: 0.13.0
- Docker Desktop: v20.10.8
```


### Anything else?

_No response_
"Timestamp": timestamp_millis(),
        "SignatureVersion": "1",
        
        
        "Signature": "EXAMPLEpH+..",
        "SigningCertURL": "https://sns.us-east-1.amazonaws.com/SimpleNotificationService-0000000000000000000000.pem",
    }
    for key in ["Subject", "SubscribeURL", "Token"]:
        if req_data.get(key):
            data[key] = req_data[key][0]
    for key in HTTP_SUBSCRIPTION_ATTRIBUTES:
        if key in subscriber:
            data[key] = subscriber[key]
    attributes = get_message_attributes(req_data)
    if attributes:
        data["MessageAttributes"] = attributes
    return json.dumps(data)
def create_sqs_message_attributes(subscriber, attributes):
    if not is_raw_message_delivery(subscriber):
        return {}
    message_attributes = {}
    for key, value in attributes.items():
        attribute = {"DataType": value["Type"]}
        if value["Type"] == "Binary":
            attribute["BinaryValue"] = base64.decodebytes(to_bytes(value["Value"]))
        else:
            attribute["StringValue"] = str(value.get("Value", ""))
        message_attributes[key] = attribute
    return message_attributes
def get_message_attributes(req_data):