### 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_
"""
        Base method for publishing the message. It is up to the child class to implement its way to publish the message
        :param context: the SnsPublishContext created by the caller, containing the necessary data to publish the
        message
        :param subscriber: the subscription data
        :return:
        """
        raise NotImplementedError
    def prepare_message(self, message_context: SnsMessage, subscriber: SnsSubscription) -> str:
        """
        Returns the message formatted in the base SNS message format. The base SNS message format is shared amongst
        SQS, HTTP(S), email-json and Firehose.
        See https://docs.aws.amazon.com/sns/latest/dg/sns-sqs-as-subscriber.html
        :param message_context: the SnsMessage containing the message data
        :param subscriber: the SNS subscription
        :return: formatted SNS message body in a JSON string
        """
        return create_sns_message_body(message_context, subscriber)
class EndpointPublisher(abc.ABC):