### 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_
last_fake_topic_char = "a" if topic_arn[-1] != "a" else "b"
        nonexistent = topic_arn[:-1] + last_fake_topic_char
        assert nonexistent != topic_arn
        test_wrong_topic_confirm_url = (
            f"{service_url}/?Action=ConfirmSubscription&TopicArn={nonexistent}&Token={token}"
        )
        wrong_topic_confirm_subscribe_request = requests.get(test_wrong_topic_confirm_url)
        snapshot.match(
            "nonexistent-token-confirm",
            _get_snapshot_requests_response(wrong_topic_confirm_subscribe_request),
        )
        # w
        subscription_attributes = aws_client.sns.get_subscription_attributes(
            SubscriptionArn=subscription_arn
        )
        assert subscription_attributes["Attributes"]["PendingConfirmation"] == "false"
        confirm_subscribe_request = requests.get(subscribe_url)
        confirm_subscribe = xmltodict.parse(confirm_subscribe_request.content)
        assert (
            confirm_subscribe["ConfirmSubscriptionResponse"]["ConfirmSubscriptionResult"][
                "SubscriptionArn"
            ]
            == subscription_arn
        )
        # a
        snapshot.match(
            "confirm-subscribe", _get_snapshot_requests_response(confirm_subscribe_request)
        )
        subscription_attributes = aws_client.sns.get_subscription_attributes(
            SubscriptionArn=subscription_arn