Rethink our caching of static (CSS, JavaScript, more?) files

Originally created by @sajolida on #16091 (Redmine)

I don’t know much about caching but in the past months we’ve had to fix 2 issues related to the long caching of CSS files. One is #16049 (closed) and the other one 4e30a3e5. As we’ll work on making our website look more fancy (and less like ikiwiki.info), I expect these issues to become more frequent.

While working on self-hosting our website, should we reconsider the caching policy for CSS to avoid or minimize such issues?

Related issues

• Related to #12408
• Related to #16128 (closed)
• Blocked by sysadmin#14588 (closed)