Add checker for namespace size usage
Part of https://gitlab.com/gitlab-org/gitlab/-/issues/209119
We need to have one single source of truth to check if a namespace exceeded the size. This service then can be re-used...
- For
git push
inPostReceiveService
- For alert banners on the Project and Group page of a namespace
- In a Job after
RootStatisticWorker
gets executed to check if the namespace should be set to read-only - In the Web IDE to alert users when the capacity exceeded.