Use `rapids-generate-version` to generate versions

[hcho3]

We cannot use rapids-generate-version yet because it relies on having at least one git tag. Use rapids-generate-version once we publish a git tag for cuForest.

[jameslamb]

Instead of avoiding the RAPIDS practices, we should just stick a v26.02.00a tag on the first commit here, so nightlies will have 26.02.* versions. I can do that for you if you'd like.

[jameslamb]

I pushed a tag:

#13 (comment)

rapids-generate-version should now do the right thing. But I won't close this until we see it actually working in CI.