feat: create gruvbox-themed nixvim configuration

Added nixvim as a flake input in flake.nix

Added plugin definitions ini home-manager/stvnliu/nixvim/

Added configuration options for easy toggling for editors

home-manager/stvnliu/editors.nix

@@ -0,0 +1,14 @@
+{
+  lib,
+  pkgs,
+  config,
+  ...
+}: {
+  imports = [
+    #./vscode.nix
+    #./intellij.nix
+  ];
+  programs.nixvim = import ./nixvim;
+  # dependencies for nixvim configuration
+  home.packages = with pkgs; [ripgrep fd];
+}