[translate.vm] give weblate permission to write to /var/lib/weblate/staging

Originally created by @emmapeel on #12340 (Redmine)

Weblate user (or maybe another user?) should be able to run ./build-website with destdir == /var/lib/weblate/staging

Parent Task: #15077 (closed)

Related issues

Edited by emmapeel
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information