### 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_
if "Name" not in kwargs:
            kwargs["Name"] = f"platform-app-{short_uid()}"
        response = aws_client.sns.create_platform_application(**kwargs)
        platform_applications.append(response["PlatformApplicationArn"])
        return response
    yield factory
    for platform_application in platform_applications:
        endpoints = aws_client.sns.list_endpoints_by_platform_application(
            PlatformApplicationArn=platform_application
        )
        for endpoint in endpoints["Endpoints"]:
            try:
                aws_client.sns.delete_endpoint(EndpointArn=endpoint["EndpointArn"])
            except Exception as e:
                LOG.debug(
                    "Error cleaning up platform endpoint '%s' for platform app '%s': %s",
                    endpoint["EndpointArn"],
                    platform_application,
                    e,
                )
        try:
            aws_client.sns.delete_platform_application(PlatformApplicationArn=platform_application)
        except Exception as e:
            LOG.debug("Error cleaning up platform application '%s': %s", platform_application, e)
class TestSNSSubscription:
    @pytest.mark.aws_validated
    def test_python_lambda_subscribe_sns_topic(
        self,
        sns_create_topic,
        sns_subscription,