299 step 3 replace service binding
Description
Because we won't rely on background service, we should replace Binding between SynchronizationService & ObserverService+FileEventListener
Technical details
implement a concurrently safe singleton as a proxy
Issues
https://gitlab.e.foundation/e/os/backlog/-/work_items/1697
https://gitlab.e.foundation/e/os/backlog/-/issues/299
10 commandments of code reviews
Edited by Vincent Bourgmayer