### 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_
subscription_token = encode_subscription_token_with_region(region=context.region)
        store.subscription_tokens[subscription_token] = subscription_arn
        
        if protocol in ["http", "https"]:
            message_ctx = SnsMessage(
                type="SubscriptionConfirmation",
                token=subscription_token,
                message=f"You have chosen to subscribe to the topic {topic_arn}.\nTo confirm the subscription, visit the SubscribeURL included in this message.",
            )
            publish_ctx = SnsPublishContext(
                message=message_ctx, store=store, request_headers=context.request.headers
            )
            self._publisher.publish_to_topic_subscriber(
                ctx=publish_ctx,
                topic_arn=topic_arn,
                subscription_arn=subscription_arn,
            )
        elif protocol not in ["email", "email-json"]:
            
            
            
            
            
            
            
            subscription["PendingConfirmation"] = "false"
            subscription["ConfirmationWasAuthenticated"] = "true"
        return SubscribeResponse(SubscriptionArn=subscription_arn)
    def tag_resource(