### 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_
self, sns_create_topic, sqs_create_queue, sqs_queue_arn, snapshot, aws_client
    ):
        topic_arn = sns_create_topic()["TopicArn"]
        queue_url = sqs_create_queue()
        queue_arn = sqs_queue_arn(queue_url)
        subscribe_resp = aws_client.sns.subscribe(
            TopicArn=topic_arn,
            Protocol="sqs",
            Endpoint=queue_arn,
            Attributes={
                "RawMessageDelivery": "true",
                "FilterPolicyScope": "MessageBody",
            },
            ReturnSubscriptionArn=True,
        )
        snapshot.match("subscribe", subscribe_resp)
        get_attrs_resp = aws_client.sns.get_subscription_attributes(
            SubscriptionArn=subscribe_resp["SubscriptionArn"]
        )
        snapshot.match("get-attrs", get_attrs_resp)
        with pytest.raises(ClientError) as e:
            wrong_sub_arn = f"{subscribe_resp['SubscriptionArn'][:-8]}{short_uid()}"
            aws_client.sns.get_subscription_attributes(SubscriptionArn=wrong_sub_arn)
        snapshot.match("get-attrs-nonexistent-sub", e.value.response)
    @pytest.mark.aws_validated
    def test_attribute_raw_subscribe(