Build Ubuntu package

[norihiro]

Description

This PR implements the packaging flow for Ubuntu.

• ONNX runtime is installed into /usr/lib/obs-virtualbg/ by following obs-backgroundremoval in AUR. Even if another package uses a different version of ONNX runtime, it should not conflict.
• Debian package is created by checkinstall. The code came from the previous obs-plugintemplate
  • License is modified to MIT since the plugin is released under MIT license.
  • The maintainer property is not implemented.
• In CMakeLists.txt, CMAKE_INSTALL_FULL_LIBDIR is not expanded to /usr/lib, I implemented another variable OBS_PLUGIN_DESTINATION that can be specified from cmake's command line.

How it has been tested

OS: Ubuntu 20.04.3 LTS. I ran this flow on Github Actions with my account, downloaded the package and installed to my Ubuntu machine on VirtualBox. And, I installed the package and confirmed the background becomes transparent.

Close #52.

[hazrpg]

I can confirm that the plugin does install from this, but the background didn't become transparent - that could just be the quality of my mic - or the ML that it might be based on. But I'm glad that the package installed though! Blend just showed my webcam as normal (no transparent background), and mask was just all black so I couldn't even mask it.

[kounoike]

@norihiro Sorry for later reply. Thanks to your contributing! I prefer CPack, so I had to rewrite it.