Write a short cookbook entry how to make use of the ConfigCacheFactory in 2.7 #5136
Description
... as soon as symfony/symfony#14178 is merged :)
Mention also:
- Ability to use a service to check for the freshness of cache entries (introduced in Symfony 2.8, see Implement service-based Resource (cache) validation symfony#15738)
ClassExistenceResource(introduced in Symfony 3.2, see Class existence resource symfony#20121)