Use mill examples in init

[pawelsadlo]

implements #3548
Modifying init to fetch examples from releases page instead of using g8 template

[pawelsadlo2]

@lihaoyi I have added some integration tests which tries to download examples from GitHub repo,
They are working locally but failing on Ci, i assume that CI can't access internet right?

[lihaoyi]

CI should be able to access the internet, not sure why it's failing

[pawelsadlo]

I have found the issue, I was relying on millVersion target to build download URLs.

But nor millVersion, neither millLastTag targets returns valid versions when runned on CI.

@lihaoyi
Is there any reliable function that return last released mill version already implemented in codebase?

[lihaoyi]

@pawelsadlo I think for the purposes of this ticket, let's skip end-to-end tests that download from Github. Those are inherently non-hermetic and we don't have the infrastructure to stand up test github instances to make them hermetic. Smaller unit tests for the various pieces of logic, and manually exercising the end to end workflow, should be enough for now