### 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_
elif req_action == "GetSubscriptionAttributes":
                sub = get_subscription_by_arn(req_data["SubscriptionArn"][0])
                if not sub:
                    return make_error(
                        message="Subscription with arn {0} not found".format(
                            req_data["SubscriptionArn"][0]
                        ),
                        code=404,
                        code_string="NotFound",
                    )
                content = "<Attributes>"
                for key, value in sub.items():
                    if key in HTTP_SUBSCRIPTION_ATTRIBUTES:
                        continue
                    content += "<entry><key>%s</key><value>%s</value></entry>\n" % (
                        key,
                        value,
                    )
                content += "</Attributes>"
                return make_response(req_action, content=content)
            elif req_action == "Subscribe":
                if "Endpoint" not in req_data:
                    return make_error(message="Endpoint not specified in subscription", code=400)
            elif req_action == "ConfirmSubscription":
                if "TopicArn" not in req_data:
                    return make_error(
                        message="TopicArn not specified in confirm subscription request",
                        code=400,
                    )
                if "Token" not in req_data: