Add new VS Code extensions to devcontainer.json

Author: Slava Katiukha

.devcontainer/devcontainer.json

@@ -8,7 +8,13 @@
     "vscode": {
       "settings": {},
       "extensions": [
-        "jetpack-io.devbox"
+        "jetpack-io.devbox",
+        "yzhang.markdown-all-in-one",
+        "streetsidesoftware.code-spell-checker",
+        "DavidAnson.vscode-markdownlint",
+        "shd101wyy.markdown-preview-enhanced",
+        "GitHub.copilot",
+        "GitHub.copilot-chat"
       ]
     }
   },