ENH: Unified interface for creating swap files?

[h-vetinari]

From #1751, where I had noted at the time:

If we're making a new switch for swap files, it would probably make sense to tie this in with conda-forge/conda-forge-ci-setup-feedstock#155 / conda-forge/conda-forge-ci-setup-feedstock#158, which is currently activated by:

azure:
  settings_win:
    variables:
      SET_PAGEFILE: "True"

I had an unmerged PR that would have allowed setting the size too, if we want to match it in capabilities with linux.

Not sure about where the PowerShell script would have to live, but IIUC, conda-smithy would just generate the call in azure-pipelines-wind.yml.tmpl, but could rely on the fact that the respective PowerShell script is present after conda-forge-ci-setup has been installed.

In contrast, the interface on linux looks like:

azure:
  settings_linux:
    swapfile_size: 15GiB

A potential unification was descoped at the time to not hold up the PR, but it would be nice to have a uniform way to do this cross-platform.

Originally posted by @h-vetinari in #1751 (comment)

[jakirkham]

This seems like a good idea

Do we see them staying roughly the same across platforms? Or do we need some escape hatch for customizing per OS?