### 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_
:raises: InvalidParameterValueException
    :return: None
    """
    for attr_name, attr in message_attributes.items():
        if len(attr_name) > 256:
            raise InvalidParameterValueException(
                "Length of message attribute name must be less than 256 bytes."
            )
        validate_message_attribute_name(attr_name)
        
        data_type = attr["DataType"]
        if data_type not in (
            "String",
            "Number",
            "Binary",
        ) and not sns_constants.ATTR_TYPE_REGEX.match(data_type):
            raise InvalidParameterValueException(
                f"The message attribute '{attr_name}' has an invalid message attribute type, the set of supported type prefixes is Binary, Number, and String."
            )
        value_key_data_type = "Binary" if data_type.startswith("Binary") else "String"
        value_key = f"{value_key_data_type}Value"
        if value_key not in attr:
            raise InvalidParameterValueException(
                f"The message attribute '{attr_name}' with type '{data_type}' must use field '{value_key_data_type}'."
            )
        elif not attr[value_key]:
            raise InvalidParameterValueException(
                f"The message attribute '{attr_name}' must contain non-empty message attribute value for message attribute type '{data_type}'.",
            )
def validate_message_attribute_name(name: str) -> None: