Maven VReg: update group statistics when creating/destroying cached responses

Context

In the world of Maven virtual registry MVC (API only interactions) (&14137 - closed), VirtualRegistries::Packages::Maven::CachedResponse holds a response from an upstream. This response is cached in GitLab and has a file that's stored in the Object Storage.

The cached responses creation and destruction should update the packages project statistic accordingly on the parent object, in this case, the (root) Group.