### Is there an existing issue for this?

- [X] I have searched the existing issues

### Feature description

SNS allows for the publishing of messages to an SMS destination with a phone number. Those messages are logged and stored in the `SnsStore`, but there is no way to retrieve them for verification. The request here is to expose a new endpoint which returns SMS messages from the store, similar to the one made available to retrieve email messages sent via SES.

### 🧑‍💻 Implementation

The `SNSServicePlatformEndpointMessagesApiResource` class makes endpoints available for accessing platform endpoint messages sent via SNS. A similar resource class could be implemented to provide new endpoints for accessing SMS messages.

Given that interaction platform endpoint messages is exposed at the path `/_aws/sns/platform-endpoint-messages`, SMS message interaction would presumably be exposed at `/_aws/sns/sms-messages`. A `GET` endpoint could accept an optional `phoneNumber` query parameter to filter messages based on the destination phone number.

```python
class SNSServiceSMSMessagesApiResource:
  @route(sns_constants.SMS_MSGS_ENDPOINT, methods=["GET"])
    def on_get(self, request: Request):
      account_id = #...
      region = #...
      filter_phone_number = request.args.get("phoneNumber")
      # get store; conditionally filter messages based on filter_phone_number
```

### Anything else?

_No response_
message_contexts = []
        for entry in publish_batch_request_entries:
            message_attributes = entry.get("MessageAttributes", {})
            if message_attributes:
                
                
                validate_message_attributes(message_attributes)
            
            if entry.get("MessageStructure") == "json":
                try:
                    message = json.loads(entry.get("Message"))
                    
                    
                    
                    message = {
                        key: field for key, field in message.items() if isinstance(field, str)
                    }
                    if "default" not in message:
                        raise InvalidParameterException(
                            "Invalid parameter: Message Structure - No default entry in JSON message body"
                        )
                    entry["Message"] = message  
                except json.JSONDecodeError:
                    raise InvalidParameterException(
                        "Invalid parameter: Message Structure - JSON message body failed to parse"
                    )
            if is_fifo := (".fifo" in topic_arn):
                if not all(["MessageGroupId" in entry for entry in publish_batch_request_entries]):
                    raise InvalidParameterException(