### 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_
SubscriptionArn=http_subscription_arn
        )
        assert subscription_attributes["Attributes"]["PendingConfirmation"] == "false"
        server.stop()
        wait_for_port_closed(server.port)
        message = "test_dlq_external_http_endpoint"
        aws_client.sns.publish(TopicArn=topic_arn, Message=message)
        response = aws_client.sqs.receive_message(QueueUrl=dlq_url, WaitTimeSeconds=3)
        assert (
            len(response["Messages"]) == 1
        ), f"invalid number of messages in DLQ response {response}"
        if raw_message_delivery:
            assert response["Messages"][0]["Body"] == message
        else:
            received_message = json.loads(response["Messages"][0]["Body"])
            assert received_message["Type"] == "Notification"
            assert received_message["Message"] == message
        receipt_handle = response["Messages"][0]["ReceiptHandle"]
        aws_client.sqs.delete_message(QueueUrl=dlq_url, ReceiptHandle=receipt_handle)
        expected_unsubscribe_url = (
            f"{service_url}/?Action=Unsubscribe&SubscriptionArn={http_subscription_arn}"
        )
        unsub_request = requests.get(expected_unsubscribe_url)
        unsubscribe_confirmation = xmltodict.parse(unsub_request.content)
        assert "UnsubscribeResponse" in unsubscribe_confirmation
        response = aws_client.sqs.receive_message(QueueUrl=dlq_url, WaitTimeSeconds=2)
        # A
        assert "Messages" not in response
    @pytest.mark.aws_validated
    def test_publish_too_long_message(self, sns_create_topic, snapshot, aws_client):