Add devcontainer configuration and update Jekyll config

* **Add devcontainer configuration**
  - Add `.devcontainer/devcontainer.json` to define the development container environment with .NET 9 SDK, Ruby 3.3, and Node LTS.
  - Include VSCode extensions and settings for the development environment.

* **Update Jekyll configuration**
  - Add `.devcontainer` to the exclude list in `docs/_config.yml`.

.devcontainer/devcontainer.json

@@ -15,10 +15,7 @@
         "ms-dotnettools.csharp",
         "rebornix.ruby",
         "streetsidesoftware.code-spell-checker",
-        "davidanson.vscode-markdownlint",
-        "esbenp.prettier-vscode",
-        "dbaeumer.vscode-eslint",
-        "ms-vscode.vscode-typescript-next"
+        "davidanson.vscode-markdownlint"
       ],
       "settings": {
         "files.autoSave": "afterDelay",