### 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_
topic_subscriptions: Dict[str, List[str]] = LocalAttribute(default=dict)
    
    subscriptions: Dict[str, SnsSubscription] = LocalAttribute(default=dict)
    
    subscription_tokens: Dict[str, str] = LocalAttribute(default=dict)
    
    sns_tags: Dict[str, List[Dict]] = LocalAttribute(default=dict)
    
    platform_endpoint_messages: Dict[str, List[Dict]] = LocalAttribute(default=dict)
    
    sms_messages: List[Dict] = LocalAttribute(default=list)
    
    subscription_filter_policy: Dict[subscriptionARN, Dict] = LocalAttribute(default=dict)
    def get_topic_subscriptions(self, topic_arn: str) -> List[SnsSubscription]:
        topic_subscriptions = self.topic_subscriptions.get(topic_arn, [])
        subscriptions = [
            subscription
            for subscription_arn in topic_subscriptions
            if (subscription := self.subscriptions.get(subscription_arn))
        ]
        return subscriptions
sns_stores = AccountRegionBundle("sns", SnsStore)