The number of forks of a project doesn't change very frequently and
running a COUNT(*) every time this information is requested can be quite
expensive. We also end up running such a COUNT(*) query at least twice
on the homepage of a project.
By caching this data and refreshing it when necessary we can reduce
project homepage loading times by around 60 milliseconds (based on the
timings of https://gitlab.com/gitlab-org/gitlab-ce).
Projects::ForkService delegates to this service almost entirely, but needed
one small change so it would propagate create errors correctly.
CreateService#execute needs significant refactoring; it is now right at the
complexity limit set by Rubocop. I avoided doing so in this commit to keep the
diff as small as possible.
Several tests depend on the insecure behaviour of ForkService, so fi them up at
the same time.
Remove overload of BaseService.initialize, so initialize gains params,
which is used to pass the namespace (like e.g. in TransferService).
The namespace is checked for permission to create projects in it.
