Add contrib integrations to home-manager module

[xlambein]

This adds home-manager options to enable specific integrations from the lib-contrib. Currently, this includes bash, zsh, fish, vim, gtk, and the Nix wallpaper for Gnome.

The module's a bit bare, it could use some more documentation. I mostly wanna know whether you're interested to upstream this :]

[Misterio77]

Sorry for the wait! Overall everything looks good, I'll see if I can add some documentation before merging.

Thanks a lot for the contribution!

[bketelsen]

subscribing so we can add this enhancement to fleek this would be awesome.

[Misterio77]

Sorry for the delay, and thanks a lot for the contribution!

---

It was my mistake to not make colorScheme more extendable... I think this would look a more neater as colorScheme.integrations, but it would either break backward compatibility (e.g. move the scheme to colorScheme.scheme) or force people to do awkward stuff such as:

{
  colorScheme = cool-scheme // {
    integrations = ...;
  };
}

An option I came up with is to move colorScheme to nix-colors.colorScheme (or maybe colors.scheme?), and the integrations would be located at nix-colors.integrations. We could then use mkRenamedOptionModule, that adds a warning while keeping it backwards compatible.

I think it would look very neat:

{ inputs, ... }:
{
  imports = [ inputs.nix-colors.homeManagerMoudules.default ];
  
  nix-colors = {
    colorScheme = inputs.nix-colors.colorSchemes.dracula;
    integrations = {
      bash.enable = true;
      vim.enable = true;
    };
  };
}

---

Another thing is that I'd love to make the integrations also have a function option to allow the user to override it with their own (while defaulting to ours). For example:

{
  colorSchemeIntegrations = {
    bash = {
      enable = true;
      function = myCustomFunction;
    };
  };
}

---

Would it be okay for you if I pushed to this PR to make these changes?

[xlambein]

Would it be okay for you if I pushed to this PR to make these changes?

Of course! :] I'm totally in line with all those changes.

[no-mood]

Any update on this? Since I'm also interested, I could help if you are too.

[lpchaim]

I've been following this for a while and thought I'd chime in, I'd love to give the proposed changes a go or assist with this however is deemed helpful.

[eureka-cpu]

I think @Misterio77 is busy w school, etc, it's been over a year since his last review. If you want to see this implemented it may just be faster to make a fork of it..

[no-mood]

I don't mean to sound rude by saying that this feature is provided by Stylix (at the time I didn't know it). In that case, misterio's nix-colors compares to base16.nix, that's used in Stylix to import a theme and set it system wide.
Thank you, Misterio, for all your tremendous work. You are the source of inspiration for so many users.