### 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.executor = ThreadPoolExecutor(num_thread, thread_name_prefix="sns_pub")
    def shutdown(self):
        self.executor.shutdown(wait=False)
    def _should_publish(
        self,
        subscription_filter_policy: dict[str, dict],
        message_ctx: SnsMessage,
        subscriber: SnsSubscription,
    ):
        """
        Validate that the message should be relayed to the subscriber, depending on the filter policy and the
        subscription status
        """
        
        
        if (
            not subscriber["PendingConfirmation"] == "false"
            and "email" not in subscriber["Protocol"]
        ):
            return