### 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_
try:
                # A
                aws_client.sns.set_subscription_attributes(
                    SubscriptionArn=subscription_arn,
                    AttributeName="RawMessageDelivery",
                    AttributeValue="true",
                )
                raise Exception("Subscription is not deleted")
            except ClientError as e:
                assert e.response["Error"]["Code"] == "NotFound"
                assert e.response["ResponseMetadata"]["HTTPStatusCode"] == 404
                snapshot.match("sub-not-found", e.response)
        retry(check_subscription_deleted, retries=10, sleep_before=0.2, sleep=3)
        subscriptions_by_topic = aws_client.sns.list_subscriptions_by_topic(TopicArn=topic_arn)
        snapshot.match("subscriptions-for-topic-after-unsub", subscriptions_by_topic)
        assert len(subscriptions_by_topic["Subscriptions"]) == 0
    @pytest.mark.aws_validated
    @pytest.mark.parametrize("content_based_deduplication", [True, False])
    def test_message_to_fifo_sqs(