[Feature] Headless browser (chrome/chromium/firefox)

I'd love if I could add a headless browser to my dev container using the dev container features.

```json
"features": {
"headless-chrome": "latest",
"headless-chromium": "latest",
"headless-firefox": "latest",
}
```

All (that I know) JS/TS testing frameworks need it. Manually adding it without having to resort to `--no-sandbox` is very complicated. I have yet to succeed at it 😞
`--no-sandbox` is considered insecure and **strongly discouraged**.

まず、リポジトリの Dev Container Features に関する規約と、feature オプションの定義方法を確認します。ユーザーが要求された feature 名を使って headless Chrome、Chromium、Firefox を追加でき、危険な workaround である --no-sandbox を必要としなくなれば完了です。

索引モデルが issue の本文から書いたものです。