Add zsh shell, enable in onizuka

nixosModules/apps/shells/zsh/default.nix

@@ -0,0 +1,20 @@
+{ config, pkgs, lib, ... }:
+
+{
+  options = {
+    zsh.enable = lib.mkEnableOption "Enables zsh";
+    zsh.setDefault = lib.mkEnableOption "Sets zsh as the default user's shell";
+  };
+
+  config = lib.mkIf config.zsh.enable {
+    programs.zsh = {
+      enable = true;
+      enableCompletion = true;
+      autosuggestions.enable = true;
+      histFile = "$HOME/.config/zsh/history";
+      histSize = 2000;
+    };
+    users.users.defaultUser.shell = lib.mkIf config.zsh.setDefault pkgs.zsh;
+    environment.shells = with pkgs; [ zsh ];
+  };
+}