Install pwsh on Windows

What does this MR do?

Installs PowerShell Core in install.ps1 on Windows. This is required by nitrile!95 (merged).

Could someone update the live version of the website as well?

Changes to public APIs

None.

Author's checklist (required)

• Intermediate commits compile (use git rebase -i main if not)
• Newly added code has a style consistent with the rest of the repository
• Newly added code is documented (guidelines)

Related issues

nitrile#24 (closed)