Ignore cache-control requests in some cases

Some caches with content preparation are skipped when the HTTP request sends a Cache-Control: no-cache (the idea being that there might still be some variation in the preparation in some cases, and we wanted to give a way to force it to not be stuck):

• templates cache
• document content XDOM
• various wiki extension content (wiki macros, panels, ui extensions, etc.)
• ...

Problem is that we noticed recently on production a high number of those cases and suspect that some bots are always sending Cache-Control: no-cache with each HTTP request, which makes the cache totally useless.

See https://forum.xwiki.org/t/cache-servletcontext-getresource/16416 for some ideas.