Implement caching mechanism

Please have a look at #2453585-16: Local Storage for Coffee →

I think it would be worth implementing object caching for the coffee AJAX callback, after working on 📌 Get coffee data only when the search box is opened Active . This could and should happen independently of local storage because the callback should be cacheable by permissions 99% of the time.

Haven't looked at implementation yet, but it might work if the AJAX request uses GET and the callback returns a cacheable response object, then potentially dynamic_page_cache could handle it with the correct cache contexts and cache tags. If there's something missing, then using VariationCache is possible in core now.