### 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_
)
        lambda_name = f"test-{short_uid()}"
        lambda_arn = create_lambda_function(
            func_name=lambda_name,
            handler_file=TEST_LAMBDA_PYTHON,
            runtime=Runtime.python3_9,
            role=lambda_su_role,
        )["CreateFunctionResponse"]["FunctionArn"]
        subscription = sns_subscription(TopicArn=topic_arn, Protocol="lambda", Endpoint=lambda_arn)
        aws_client.sns.set_subscription_attributes(
            SubscriptionArn=subscription["SubscriptionArn"],
            AttributeName="RedrivePolicy",
            AttributeValue=json.dumps({"deadLetterTargetArn": dlq_arn}),
        )
        response_attributes = aws_client.sns.get_subscription_attributes(
            SubscriptionArn=subscription["SubscriptionArn"]
        )
        snapshot.match("subscription-attributes", response_attributes)
        aws_client.awslambda.delete_function(FunctionName=lambda_name)
        aws_client.sns.publish(
            TopicArn=topic_arn,
            Message="test_redrive_policy",
            MessageAttributes={"attr1": {"DataType": "Number", "StringValue": "1"}},
        )
        response = aws_client.sqs.receive_message(
            QueueUrl=dlq_url, WaitTimeSeconds=10, MessageAttributeNames=["All"]
        )
        snapshot.match("messages", response)
    @pytest.mark.aws_validated
    def test_publish_with_empty_subject(self, sns_create_topic, snapshot, aws_client):