Docs: Re-organize conceptual docs (#27047)

Reorganization of conceptual documentation

---------

Co-authored-by: Lance Martin <122662504+rlancemartin@users.noreply.github.com>
Co-authored-by: Lance Martin <lance@langchain.dev>
Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>
Co-authored-by: Bagatur <22008038+baskaryan@users.noreply.github.com>

docs/sidebars.js

@@ -47,7 +47,17 @@ module.exports = {
         className: 'hidden',
       }],
     },
-    "concepts",
+    {
+      type: "category",
+      link: {type: 'doc', id: 'concepts/index'},
+      label: "Conceptual Guide",
+      collapsible: false,
+      items: [{
+        type: 'autogenerated',
+        dirName: 'concepts',
+        className: 'hidden',
+      }],
+    },
     {
       type: "category",
       label: "Ecosystem",