Continuation of #20102

Now that we have a on-demand cibuildwheel process for x86, we should

• upload weekly to https://anaconda.org/scipy-wheels-nightly/numpy and https://anaconda.org/multibuild-wheels-staging/numpy for releases
• document the process at https://numpy.org/devdocs/dev/releasing.html
• add missing wheels for windows 32/64 and PyPy (window-64 done in PR 20383, PyPy done in PR 20565)

I think @charris would prefer to release the upcoming 1.22 via the current process, but once that is out we should move to this workflow.

@thomasjpfan thoughts?