### 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_
_requests.put(request)
            return Response(status=429)
        number_of_endpoints = 4
        servers = []
        try:
            for _ in range(number_of_endpoints):
                server = HTTPServer()
                server.start()
                servers.append(server)
                server.expect_request("/").respond_with_handler(handler)
                http_endpoint = server.url_for("/")
                wait_for_port_open(http_endpoint)
                sns_subscription(TopicArn=topic_arn, Protocol="http", Endpoint=http_endpoint)
            # f
            subscription_list = aws_client.sns.list_subscriptions_by_topic(TopicArn=topic_arn)
            assert subscription_list["ResponseMetadata"]["HTTPStatusCode"] == 200
            assert (
                len(subscription_list["Subscriptions"]) == number_of_endpoints
            ), f"unexpected number of subscriptions {subscription_list}"
            tokens = []
            for _ in range(number_of_endpoints):
                request = _requests.get(timeout=2)
                request_data = request.get_json(True)
                tokens.append(request_data["Token"])
                assert request_data["TopicArn"] == topic_arn