plugins: add and configure zen-mode and twilight

Co-Authored-by: iGor milhit <igor@milhit.ch>

lua/custom/plugins/zen-mode.lua

@@ -0,0 +1,26 @@
+--  Zen mode with twilight.
+--    Improves the edition experience with distraction free feature.
+
+return {
+  "folke/zen-mode.nvim",
+  -- Twilight allows to dim text outside of the cursor line.
+  dependencies = {
+    "folke/twilight.nvim",
+    opts = {
+      -- Set the context to null in order to avoid highlighting to much
+      -- paragraphs in markdown.
+      context = 0,
+    },
+  },
+  opts = {
+    window = {
+      -- Set the window width (85 columns) and height (80%).
+      width = 85,
+      height = .8,
+      options = {
+        -- Disable line numbering.
+        number = false,
+      },
+    },
+  },
+}