Add indent-blankline.nvim and mini-indentscope

Basically it just highlights tabs, see
lukas-reineke/indent-blankline.nvim#649 (comment)

home-manager/nvim/plugins.nix

@@ -1,4 +1,10 @@
-{pkgs, ...}: {
+{
+  pkgs,
+  inputs,
+  ...
+}: let
+  nixvimHelpers = inputs.nixvim.lib.x86_64-linux.helpers;
+in {
   programs.nixvim = {
     plugins = {
       transparent.enable = true;
@@ -110,6 +116,18 @@
             # cursor location to LINE:COLUMN
             section_location = "%2l:%-2v";
           };
+          indentscope = {
+            draw = {
+              delay = 0;
+              animation = nixvimHelpers.mkRaw "function() return 0 end"; # disable animation
+              priority = 2;
+            };
+            options = {
+              try_as_border = true;
+              border = "top";
+            };
+            symbol = "▎";
+          };
         };
       };
       # Highlight, edit, and navigate code
@@ -136,6 +154,19 @@
         enable = true;
         theme = "startify";
       };
+      indent-blankline = {
+        enable = true;
+        settings = {
+          indent = {
+            smart_indent_cap = false;
+            priority = 1;
+          };
+          scope = {
+            show_start = false;
+            show_end = false;
+          };
+        };
+      };
     };
     extraPlugins = with pkgs.unstable.vimPlugins; [
       vim-sleuth # Detect tabstop and shiftwidth automatically