### 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_
snapshot.match("messages", messages)
    @pytest.mark.only_localstack
    def test_redrive_policy_http_subscription(
        self, sns_create_topic, sqs_create_queue, sqs_queue_arn, sns_subscription, aws_client
    ):
        dlq_name = f"dlq-{short_uid()}"
        dlq_url = sqs_create_queue(QueueName=dlq_name)
        dlq_arn = sqs_queue_arn(dlq_url)
        topic_arn = sns_create_topic()["TopicArn"]
        # c
        with HTTPServer() as server:
            server.expect_request("/subscription").respond_with_data(b"", 200)
            http_endpoint = server.url_for("/subscription")
            wait_for_port_open(server.port)
            subscription = sns_subscription(
                TopicArn=topic_arn, Protocol="http", Endpoint=http_endpoint
            )
            aws_client.sns.set_subscription_attributes(
                SubscriptionArn=subscription["SubscriptionArn"],
                AttributeName="RedrivePolicy",
                AttributeValue=json.dumps({"deadLetterTargetArn": dlq_arn}),
            )
            # w
            poll_condition(lambda: len(server.log) >= 1, timeout=10)
            request, _ = server.log[0]
            event = request.get_json(force=True)
            assert request.path.endswith("/subscription")
            assert event["Type"] == "SubscriptionConfirmation"
            assert event["TopicArn"] == topic_arn
            aws_client.sns.confirm_subscription(TopicArn=topic_arn, Token=event["Token"])