Support Unity UPM packages

[KuraiAndras]

The unity ecosystem is slowly moving towards package management with its UPM (Unity Package Manager) format. Even tough the asset store does not yet fully support them, git repositories are supported, and there are also community driven UPM repositories which are getting more and more tracksion (for example https://openupm.com). Also NuGet packages can be installed via the Xoofx UnityNuGet UPM server project.

Getting dependabot support would be a huge plus. On the technical side I suppose it would not require too much work, since UPM is mostly just a rebranding of NPM.