Integrate with node-problem-detector

# Background

Currently kdebug works as a command-line tool. Also it requires direct machine access like SSH. If we could extend it's form, for example, to be part of monitoring system, there should be more interesting use cases.

# Design
[node-problem-detector](https://github.com/kubernetes/node-problem-detector) is an official Kubernetes project. It runs as a daemon process on each node and can report various node problems to various data sinks.

It supports custom plugins which can invoke any external programs. We can integrate with this and become part of its monitoring ecosystem.

# Works

* Return non-zero exit code in case of problems.
* Support a short message formatted, as NPD has a limitation of message length.
* Have doc/examples for how to deploy