move vscode extensions to recommended location

Author: ManfredLange

.devcontainer/devcontainer.json

@@ -5,12 +5,16 @@
    ],
    "service": "dev-php",
    "workspaceFolder": "/src",
-   "extensions": [
-      "eamodio.gitlens",
-      "editorconfig.editorconfig",
-      "k--kato.docomment",
-      "shd101wyy.markdown-preview-enhanced"
-   ],
+   "customizations": {
+      "vscode": {
+         "extensions": [
+            "eamodio.gitlens",
+            "editorconfig.editorconfig",
+            "k--kato.docomment",
+            "shd101wyy.markdown-preview-enhanced"
+         ]
+      }
+   },
    "remoteUser": "dev",
    "shutdownAction": "stopCompose"
 }