Add devcontainer (#476)

* Add devcontainer

* Add extensions file

Author: theletterf

.devcontainer/devcontainer.json

@@ -0,0 +1,13 @@
+{
+  // You can have other configurations here
+  "image": "mcr.microsoft.com/devcontainers/universal:latest",
+
+  // This is the key part for adding extensions
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "Elastic.elastic-docs-v3-utilities"
+      ]
+    }
+  }
+}

.vscode/extensions.json

@@ -0,0 +1,5 @@
+{
+  "recommendations": [
+    "Elastic.elastic-docs-v3-utilities"
+  ]
+}