### 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_
message_attributes: MessageAttributeMap,
) -> Dict[str, Dict[str, str]]:
    attributes = {}
    if not message_attributes:
        return attributes
    
    
    for attr_name, attr in message_attributes.items():
        data_type = attr["DataType"]
        if data_type.startswith("Binary"):
            
            
            val = base64.b64encode(attr["BinaryValue"]).decode()
        else:
            val = attr.get("StringValue")
        attributes[attr_name] = {
            "Type": data_type,
            "Value": val,
        }
    return attributes
def is_raw_message_delivery(subscriber: SnsSubscription) -> bool:
    return subscriber.get("RawMessageDelivery") in ("true", True, "True")
def is_fifo_topic(subscriber: SnsSubscription) -> bool:
    return subscriber.get("TopicArn", "").endswith(".fifo")
def store_delivery_log(