### 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_
timeout=5,
        )
        unsub_request, _ = server.log[2]
        payload = unsub_request.get_json(force=True)
        assert payload["Type"] == "UnsubscribeConfirmation"
        assert unsub_request.headers["x-amz-sns-message-type"] == "UnsubscribeConfirmation"
        assert "Signature" in payload
        assert "SigningCertURL" in payload
        token = payload["Token"]
        assert payload["URL"] == (
            f"{service_url}/?" f"Action=ConfirmSubscription&TopicArn={topic_arn}&Token={token}"
        )
        snapshot.match("unsubscribe-request", payload)
    @pytest.mark.only_localstack
    @pytest.mark.parametrize("raw_message_delivery", [True, False])
    def test_dlq_external_http_endpoint(
        self,
        sns_create_topic,
        sqs_create_queue,
        sqs_queue_arn,
        sns_subscription,
        sns_create_http_endpoint,
        sns_create_s,
        sns_allow_topic_sqs_queue,
        raw_message_delivery,
        aws_client,
    ):
        # N
        topic_arn, http_subscription_arn, endpoint_url, server = sns_create_http_endpoint(
            raw_message_delivery