### 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_
"TopicArn": topic_arn,
                "Message": message,
            },
        )
        json_response = xmltodict.parse(response.content)
        json_response["Response"].pop("@xmlns")
        json_response["Response"]["ResponseMetadata"][
            "HTTPStatusCode"
        ] = response.status_code
        json_response["Response"]["ResponseMetadata"]["HTTPHeaders"] = dict(response.headers)
        snapshot.match("post-request", json_response)
        assert response.status_code == 200
        assert b"<Response" in response.content
        rs = aws_client.sqs.receive_message(
            QueueUrl=queue_url, VisibilityTimeout=0, WaitTimeSeconds=5
        )
        snapshot.match("messages", rs)
        msg_body = json.loads(rs["Messages"][0]["Body"])
        assert msg_body["TopicArn"] == topic_arn
        assert msg_body["Message"] == message
    @pytest.mark.only_localstack
    def test_multiple_subscriptions_http_endpoint(
        self, sns_create_topic, sns_subscription, aws_client
    ):
        # c
        topic_arn = sns_create_topic()["TopicArn"]
        # b
        _requests = queue.Queue()
        # c
        def handler(request):