docs: add upgrade guide for 1.3.8 (#2170)

* add upgrade guide for 1.3.8

* added to sidebar

* added announcement bar

www/docs/sidebars.js

@@ -169,6 +169,11 @@ module.exports = {
               id: "advanced/backend/upgrade-guides/1-3-6",
               label: "v1.3.6"
             },
+            {
+              type: "doc",
+              id: "advanced/backend/upgrade-guides/1-3-8",
+              label: "v1.3.8"
+            },
           ]
         },
       ]