Collect MSI logs by default, relay & respect exit codes as specified in info.json

[fasterthanlime]

install_prereqs_windows.go is in pretty good shape right now, but I don't see any exit code handling.

As far as I can tell, cmd.Run() will return an error if there's a non-zero exit code (even though, with MSIs/.exe installers, many exit codes might indicate success, not just 0). The redist file format already accomodates for that: https://github.com/itchio/butler/blob/master/redist/types.go

Additionally, I want MSI installs (which are particularly fiddly) to collect logs by default and the itch app to relay those (in case it failed) in the cave logs so that when reported by the automatic installer, we can see what was going on.

See https://github.com/itchio/itch/issues/1304 and https://github.com/itchio/itch-compatibility-watchlist/issues/1049

[fasterthanlime]

Battle plan:

• [ ] ~Use MsiOpenPackage and MsiEnumProducts to find out if an MSI is already installed~
• [ ] ~If it is, run with /fpmsu instead of /i~
  • ~This will work even if the .msi was initially installed from somewhere else~
• [ ] ~If it's not, run with /i as usual (but relay exit code and logs if it fails.~

Use https://github.com/winlabs/gowin32/ to use the win32 API for MSIs directly.