docs: added plugins documentation (#10989)

(Should be merged after the next release)

Closes DX-1294

www/apps/book/sidebar.mjs

@@ -106,6 +106,11 @@ export const sidebar = sidebarAttachHrefCommonOptions([
           },
         ],
       },
+      {
+        type: "link",
+        title: "Re-Use Customizations",
+        path: "/learn/customization/reuse-customizations",
+      },
       {
         type: "link",
         title: "Next Steps",
@@ -458,6 +463,18 @@ export const sidebar = sidebarAttachHrefCommonOptions([
           },
         ],
       },
+      {
+        type: "link",
+        path: "/learn/fundamentals/plugins",
+        title: "Plugins",
+        children: [
+          {
+            type: "link",
+            path: "/learn/fundamentals/plugins/create",
+            title: "Create Plugin",
+          },
+        ],
+      },
       {
         type: "link",
         path: "/learn/fundamentals/custom-cli-scripts",