### 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_
AttributeName="RawMessageDelivery",
            AttributeValue="false",
        )
        publish_response = aws_client.sns.publish(
            TopicArn=topic_arn,
            Message="text",
            MessageAttributes=attributes,
        )
        snapshot.match("publish-msg-json", publish_response)
        msg = aws_client.sqs.receive_message(
            QueueUrl=queue_url,
            AttributeNames=["All"],
            MessageAttributeNames=["All"],
            WaitTimeSeconds=3,
        )
        snapshot.match("json-delivery-msg-attrs", msg)
        # b
        # h
    @pytest.mark.only_localstack
    @pytest.mark.aws_validated
    @pytest.mark.parametrize("raw_message_delivery", [True, False])
    def test_subscribe_external_http_endpoint(
        self, sns_create_http_endpoint, raw_message_delivery, aws_client, snapshot
    ):
        def _get_snapshot_requests_response(response: requests.Response) -> dict:
            parsed_xml_body = xmltodict.parse(response.content)
            for root_tag, fields in parsed_xml_body.items():
                fields.pop("@xmlns", None)
                if "ResponseMetadata" in fields:
                    fields["ResponseMetadata"]["HTTPHeaders"] = dict(response.headers)