### 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_
sms_messages = sns_backend.sms_messages
            for contact in list_of_contacts:
                sms_was_found = False
                for message in sms_messages:
                    if message["endpoint"] == contact:
                        sms_was_found = True
                        break
                assert sms_was_found
        retry(check_messages, sleep=0.5)
    @pytest.mark.aws_validated
    def test_publish_wrong_phone_format(
        self, sns_create_topic, sns_subscription, snapshot, aws_client
    ):
        message = "Good news everyone!"
        with pytest.raises(ClientError) as e:
            aws_client.sns.publish(Message=message, PhoneNumber="+1a234")
        snapshot.match("invalid-number", e.value.response)
        with pytest.raises(ClientError) as e:
            aws_client.sns.publish(Message=message, PhoneNumber="NAA+15551234567")
        snapshot.match("wrong-format", e.value.response)
        topic_arn = sns_create_topic()["TopicArn"]
        with pytest.raises(ClientError) as e:
            sns_subscription(TopicArn=topic_arn, Protocol="sms", Endpoint="NAA+15551234567")
        snapshot.match("wrong-endpoint", e.value.response)
    @pytest.mark.aws_validated
    def test_publish_wrong_arn_format(self, snapshot, aws_client):