Add support for WSL

[VoxelPrismatic]

For some reason, system("uname") returns an empty string. I added a check for this.

This also resolves #433

There are errors printed now, but that is from the server when unauthorized.

[CLAassistant]

All committers have signed the CLA.

[saranshsaini]

Hey, just noticed that the check for mac is has('darwin') but the docs for the "has" function seem to use 'mac' ie. it should be has('mac'). Can you double check whether that is the case?

[saranshsaini]

Thanks, looks good. One last thing, could you add a quick comment explaining why specifically this was necessary? Saw in your nvim config files that you were previously explicitly setting vim.g.codeium_os to "Linux" in your init.lua file. Does the change you made in this PR fix that (as in, do you still need to set the codeium_os explicitly in your init file)?

[VoxelPrismatic]

Actually, I was looking through the code and tried setting that option to no avail. I just assumed I was setting it wrong and wanted to fix the code regardless.