Template option for only caching loaders when not in DEBUG

[SmileyChris]

Since Django 4.1, the cached loader is default, and includecontents follows the same pattern.
In debug though, it's probably nicer not to have the templates cached so you can edit them and actually see the updates without any code changes (which reloads the server).

A boolean loader option, callled cached_loader_unless_debug or something would be a nice way to allow this. See the dance that you normally have to do in #2

(Also it should probably be an error to specify this option if you're also passing loaders manually)