Bucket of Staging files after deploying an app engine : <p>After deploying a google app engine, at least 4 buckets are created in the google cloud storage:</p>

<ul>
<li>[project-id].appspot.com</li>
<li>staging.[project-id].appspot.com</li>
<li>artifacts.[project-id].appspot.com</li>
<li>vm-containers.[project-id].appspot.com</li>
</ul>

<p>What are they, and will they incur storage cost? Can they be safely deleted?</p>
