### 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_
)
        aws_client.sns.unsubscribe(SubscriptionArn=test_subscription_arn)
        # w
        time.sleep(1)
        # c
        subscriptions = aws_client.sns.list_subscriptions_by_topic(TopicArn=topic_arn)
        snapshot.match("subscriptions", subscriptions)
        # s
        aws_client.sns.set_subscription_attributes(
            SubscriptionArn=subscription_arn,
            AttributeName="RedrivePolicy",
            AttributeValue=json.dumps({"deadLetterTargetArn": dlq_arn}),
        )
        sub_attrs = aws_client.sns.get_subscription_attributes(SubscriptionArn=subscription_arn)
        snapshot.match("subscriptions-attrs-with-redrive", sub_attrs)
        # A
        assert poll_condition(lambda: not sqs_queue_exists(queue_url), timeout=5)
        # t
        for i in range(2):
            message = f"test_dlq_after_sqs_endpoint_deleted_{i}"
            aws_client.sns.publish(TopicArn=topic_arn, Message=message)
            response = aws_client.sqs.receive_message(
                QueueUrl=dlq_url, WaitTimeSeconds=10, MaxNumberOfMessages=4
            )
            aws_client.sqs.delete_message(
                QueueUrl=dlq_url, ReceiptHandle=response["Messages"][0]["ReceiptHandle"]
            )
            snapshot.match(f"message-{i}-after-delete", response)
    @pytest.mark.aws_validated
    def test_publish_to_firehose_with_s3(