### 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_
topic_arn = sns_create_topic()["TopicArn"]
        # T
        # m
        with pytest.raises(ClientError) as e:
            message = json.dumps({"sqs": "Test message"})
            aws_client.sns.publish(
                TopicArn=topic_arn,
                Message=message,
                MessageStructure="json",
            )
        snapshot.match("missing-default-key", e.value.response)
        # i
        with pytest.raises(ClientError) as e:
            message = '{"default": "This is a default message"} }'
            aws_client.sns.publish(
                TopicArn=topic_arn,
                Message=message,
                MessageStructure="json",
            )
        snapshot.match("invalid-json", e.value.response)
        # d
        # h
        # `
        message = '{"default": "This is a default message", "default": "Duplicate"}'
        resp = aws_client.sns.publish(
            TopicArn=topic_arn,
            Message=message,