feat: add toggleterm, markdown preview keymaps, lualine switch filename and navic (#23)

- Configured toggleterm plugin
- Added keymap for markdown preview
- Changed lualine so Navic is better readable by switching filename and
type with Navic.

config/plugins/utils/toggleterm.nix

@@ -0,0 +1,42 @@
+_: {
+  plugins.toggleterm = {
+    enable = true;
+    settings = {
+      size = 20;
+    };
+  };
+  keymaps = [
+    {
+      mode = "n";
+      key = "<leader>t";
+      action = "<cmd>ToggleTerm<cr>";
+      options = {
+        desc = "Toggle Terminal Window";
+      };
+    }
+    {
+      mode = "n";
+      key = "<leader>tv";
+      action = "<cmd>ToggleTerm direction=vertical<cr>";
+      options = {
+        desc = "Toggle Vertical Terminal Window";
+      };
+    }
+    {
+      mode = "n";
+      key = "<leader>th";
+      action = "<cmd>ToggleTerm direction=horizontal<cr>";
+      options = {
+        desc = "Toggle Horizontal Terminal Window";
+      };
+    }
+    {
+      mode = "n";
+      key = "<leader>tf";
+      action = "<cmd>ToggleTerm direction=float<cr>";
+      options = {
+        desc = "Toggle Floating Terminal Window";
+      };
+    }
+  ];
+}