Made it a Check_MK Plugin

Check_MK ships a [VBS plugin](https://github.com/ypid-bot/check_mk/blob/master/agents/windows/plugins/windows_updates.vbs) which was quite tricky to setup and was not reliable for me so I adopted this PowerShell script to make it a drop-in replacement for [windows_updates.vbs](https://github.com/ypid-bot/check_mk/blob/master/agents/windows/plugins/windows_updates.vbs).

https://github.com/ypid-bot/check_mk/pull/7
https://github.com/ypid/check_mk/blob/feature/windows_updates.ps1/agents/windows/plugins/windows_updates.ps1