feat: change the default shell to zsh

Reviewed-on: #59

common/default.nix

@@ -7,5 +7,6 @@
     ./raito-proxy-aware-nginx.nix
     ./raito-vm.nix
     ./sysadmin
+    ./zsh.nix
   ];
 }

common/zsh.nix

@@ -0,0 +1,16 @@
+{ lib, pkgs, config, ... }: {
+  users.defaultUserShell = pkgs.zsh;
+  programs.zsh = {
+    enable = true;
+    enableCompletion = true;
+    autosuggestions.enable = true;
+    interactiveShellInit = ''
+      ${lib.getExe pkgs.nix-your-shell} zsh | source /dev/stdin
+    '';
+    promptInit = ''
+      # https://grml.org/zsh/grml-zsh-refcard.pdf
+      source ${pkgs.grml-zsh-config}/etc/zsh/zshrc
+      PS1='%n@${config.networking.fqdn} %/ \$ '
+    '';
+  };
+}