### 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,
        context: RequestContext,
        subscription_arn: subscriptionARN,
        attribute_name: attributeName,
        attribute_value: attributeValue = None,
    ) -> None:
        store = self.get_store(account_id=context.account_id, region_name=context.region)
        sub = store.subscriptions.get(subscription_arn)
        if not sub:
            raise NotFoundException("Subscription does not exist")
        validate_subscription_attribute(
            attribute_name=attribute_name,
            attribute_value=attribute_value,
            topic_arn=sub["TopicArn"],
        )
        try:
            call_moto(context)
        except CommonServiceException as e:
            
            if e.code == "InvalidParameter":
                raise InvalidParameterException(e.message)
            raise
        if attribute_name == "FilterPolicy":
            store = self.get_store(account_id=context.account_id, region_name=context.region)
            store.subscription_filter_policy[subscription_arn] = json.loads(attribute_value)
        sub[attribute_name] = attribute_value
    def confirm_subscription(