Update MicroKernelTrait directory structure #6868
Description
Micro kernel documentation (https://symfony.com/doc/current/configuration/micro_kernel_trait.html) states that it uses "traditional Symfony application" structure, but since Symfony 3 we have different default locations for logs/ and cache/ (https://symfony.com/doc/current/configuration/override_dir_structure.html).
We should add getLogDir() and getCacheDir() override examples to fit new directory structure.