### 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_
self, message_context: SnsMessage, subscriber: SnsSubscription
    ) -> Union[str, Dict]:
        endpoint_arn = subscriber["Endpoint"]
        platform_type = get_platform_type_from_endpoint_arn(endpoint_arn)
        return {
            "TargetArn": endpoint_arn,
            "TopicArn": subscriber["TopicArn"],
            "SubscriptionArn": subscriber["SubscriptionArn"],
            "Message": message_context.message_content(protocol=platform_type),
            "MessageAttributes": message_context.message_attributes,
            "MessageStructure": message_context.message_structure,
            "Subject": message_context.subject,
        }
    @staticmethod
    def _legacy_publish_to_gcm(context: SnsPublishContext, endpoint: str):
        application_attributes, endpoint_attributes = get_attributes_for_application_endpoint(
            endpoint
        )
        send_message_to_gcm(
            context=context,
            app_attributes=application_attributes,
            endpoint_attributes=endpoint_attributes,
        )
class SmsTopicPublisher(TopicPublisher):