[Feature] Mill support (for project import)

[idanarye]

Mill is starting to position itself as the next build system for JVM projects. I think supporting Mill projects should at least be in the roadmap.

[strangepleasures]

Thank you for your suggestion. While our team's priority at the moment is to provide great support for the most popular build systems, we are planning to provide an API allowing external collaborators to write integrations with other build systems. Let us know if you would be interested.