### 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_
"default": "This is the default message which must be present when publishing a message to a topic.",
            "APNS": '{"aps":{"alert": "Check out these awesome deals!","url":"www.amazon.com"} }',
            "GCM": '{"data":{"message":"Check out these awesome deals!","url":"www.amazon.com"}}',
        }
        # p
        aws_client.sns.publish(
            TopicArn=topic_arn,
            Message=json.dumps(message),
            MessageStructure="json",
        )
        sns_backend = SnsProvider.get_store(TEST_AWS_ACCOUNT_ID, TEST_AWS_REGION_NAME)
        platform_endpoint_msgs = sns_backend.platform_endpoint_messages
        # a
        def check_message():
            assert len(platform_endpoint_msgs[endpoint_arn]) > 0
        retry(check_message, retries=PUBLICATION_RETRIES, sleep=PUBLICATION_TIMEOUT)
        # e
        assert platform_endpoint_msgs[endpoints_arn["GCM"]][0]["Message"] == message["GCM"]
        assert platform_endpoint_msgs[endpoints_arn["APNS"]][0]["Message"] == message["APNS"]
    @pytest.mark.aws_validated
    def test_message_attributes_prefixes(
        self, sns_create_s, sns_create_topic, sqs_create_queue, snapshot, aws_client
    ):
        topic_arn = sns_create_topic()["TopicArn"]
        queue_url = sqs_create_queue()
        sns_create_s(topic_arn=topic_arn, queue_url=queue_url)
        with pytest.raises(ClientError) as e:
            aws_client.sns.publish(
                TopicArn=topic_arn,
                Message="test message",