Blocking customizations from users using webdav

Change on deployment configuration to deny adding customizations through the webdav container. Necessary for:

• https://cern.service-now.com/service-portal?id=outage&n=OTG0149421
• https://cern.service-now.com/service-portal?id=outage&n=OTG0149420

Closes: drupal-operations#11 (closed)