feature: Add extras.lang.NuShell

[gplusplus314]

Did you check the docs?

• I have read all the LazyVim docs

Is your feature request related to a problem? Please describe.

Not really a problem, no. But LSP and CMP configuration is just a bit complicated.

Describe the solution you'd like

I really love the concept of the extras.lang.* packages and it's my favorite aspect of LazyVim. It would be really great if we could add NuShell (the "nu" language) to LazyVim so that it "just works", like the other supported languages.

Describe alternatives you've considered

Manually configuring the LSP and autocomplete. To be honest, I haven't been successful at this unless I use vanilla NeoVim from scratch - I always end up breaking something in LazyVim.

Additional context

There's an official nvim-lspconfig here.