Publish alpha(s) and nightly on https://anaconda.org/scientific-python-nightly-wheels/

[Carreau]

Downstream users have requested wether we can do alpha to test new features (even if unstable).

I think we should also have nightly on scientific Python anaconda index

[Carreau]

Should be working now; we might just want to update the nighlty cron to only upload the main branch, and mark the version number as .dev

[Carreau]

I think we need to run hatch version dev, but I don't know how to have the number after .dev monotonically increased.

hatch version "7.0.0a1.dev$(git rev-list --count v7.0.0a0..HEAD)"

Maybe ?