pulumi: install providers and add update script

Without providers (also called plugins) pulumi doesn't do much. The way
they work, if you want to use a provider, pulimi will look for it in
your PATH, and if not found it will download it. Providers are just
executables, but third party binaries usually don't work on nixos unless
they are patched with the patchelf utility. Because of that, I'm
installing some patched providers with the main pulumi binary.

I'm also adding a small script helper to generate the hashes for all the
binaries.