### 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_
context: SnsPublishContext, app_attributes: Dict[str, str], endpoint_attributes: Dict[str, str]
) -> None:
    """
    Send the message directly to GCM, with the credentials used when creating the PlatformApplication and the Endpoint
    :param context: SnsPublishContext
    :param app_attributes: ApplicationPlatform attributes, contains PlatformCredential for GCM
    :param endpoint_attributes: Endpoint attributes, contains Token that represent the mobile endpoint
    :return:
    """
    server_key = app_attributes.get("PlatformCredential", "")
    token = endpoint_attributes.get("Token", "")
    
    json_message = context.message.message_content("GCM")
    data = json.loads(json_message)
    data["to"] = token
    headers = {"Authorization": f"key={server_key}", "Content-type": "application/json"}
    response = requests.post(
        sns_constants.GCM_URL,
        headers=headers,
        data=json.dumps(data),
    )
    if response.status_code != 200:
        LOG.warning(
            f"Platform GCM returned response {response.status_code} with content {response.content}"
        )
def create_sns_message_body(message_context: SnsMessage, subscriber: SnsSubscription) -> str: