### 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_
_, queue_arn, queue_url = self._create_queue()
        # p
        subscription = self._publish_sns_message_with_attrs(queue_arn, "sqs")
        # a
        def check_message():
            messages = self.sqs_client.receive_message(QueueUrl=queue_url, VisibilityTimeout=0)[
                "Messages"
            ]
            self.assertEqual(
                json.loads(messages[0]["Body"])["MessageAttributes"]["attr1"]["Value"],
                "99.12",
            )
        retry(check_message, retries=PUBLICATION_RETRIES, sleep=PUBLICATION_TIMEOUT)
        # c
        self.sqs_client.delete_queue(QueueUrl=queue_url)
        self.sns_client.unsubscribe(SubscriptionArn=subscription["SubscriptionArn"])
    def test_subscribe_platform_endpoint(self):
        sns = self.sns_client
        sns_backend = SNSBackend.get()
        app_arn = sns.create_platform_application(Name="app1", Platform="p1", Attributes={})[
            "PlatformApplicationArn"
        ]
        platform_arn = sns.create_platform_endpoint(
            PlatformApplicationArn=app_arn, Token="token_1"
        )["EndpointArn"]
        subscription = self._publish_sns_message_with_attrs(platform_arn, "application")
        # a
        def check_message():