By default schedulers should be executed with the user who installed the extension

We provide a configuration to allow specifying the user to use for executing the change request schedulers, and we specify that when not set the fallback is to use superadmin user.
This choice is not really good since superadmin notifications are hidden.
Instead we should just fallback on the user who installed the extensions: that's the user who install the schedulers documents, so it's the default context user for the execution of schedulers.