### 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_
"""
        external_url = external_service_url("sns")
        unsubscribe_url = create_unsubscribe_url(external_url, subscriber["SubscriptionArn"])
        message_attributes = prepare_message_attributes(message_context.message_attributes)
        event = {
            "Records": [
                {
                    "EventSource": "aws:sns",
                    "EventVersion": "1.0",
                    "EventSubscriptionArn": subscriber["SubscriptionArn"],
                    "Sns": {
                        "Type": message_context.type or "Notification",
                        "MessageId": message_context.message_id,
                        "TopicArn": subscriber["TopicArn"],
                        "Subject": message_context.subject,
                        "Message": message_context.message_content(subscriber["Protocol"]),
                        "Timestamp": timestamp_millis(),
                        "SignatureVersion": "1",
                        
                        
                        "Signature": "EXAMPLEpH+..",
                        "SigningCertUrl": "https://sns.us-east-1.amazonaws.com/SimpleNotificationService-0000000000000000000000.pem",
                        "UnsubscribeUrl": unsubscribe_url,
                        "MessageAttributes": message_attributes,
                    },
                }
            ]
        }
        return json.dumps(event)
class SqsTopicPublisher(TopicPublisher):