### 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_
raise NotFoundException("Endpoint not specified in subscription")
        if protocol not in sns_constants.SNS_PROTOCOLS:
            raise InvalidParameterException(
                f"Invalid parameter: Amazon SNS does not support this protocol string: {protocol}"
            )
        elif protocol in ["http", "https"] and not endpoint.startswith(f"{protocol}://"):
            raise InvalidParameterException(
                "Invalid parameter: Endpoint must match the specified protocol"
            )
        elif protocol == "sms" and not is_e164(endpoint):
            raise InvalidParameterException(f"Invalid SMS endpoint: {endpoint}")
        elif protocol == "sqs":
            try:
                parse_arn(endpoint)
            except InvalidArnException:
                raise InvalidParameterException("Invalid parameter: SQS endpoint ARN")
        if ".fifo" in endpoint and ".fifo" not in topic_arn:
            raise InvalidParameterException(
                "Invalid parameter: Invalid parameter: Endpoint Reason: FIFO SQS Queues can not be subscribed to standard SNS topics"
            )
        elif ".fifo" in topic_arn and ".fifo" not in endpoint:
            raise InvalidParameterException(
                "Invalid parameter: Invalid parameter: Endpoint Reason: Please use FIFO SQS queue"
            )
        if attributes:
            for attr_name, attr_value in attributes.items():
                validate_subscription_attribute(
                    attribute_name=attr_name, attribute_value=attr_value, topic_arn=topic_arn
                )