CPAlgorithms: two fixes for the global trigger SFs

!70292 (merged) introduced the new option multiTriggerChainsPerYear which is unfortunately currently preventing the global trigger SF config block from being set up properly: the first commit in this MR addresses that.

The second issue is that single-electron trigger SFs are not retrieved properly (zero effect of systematics). This is fixed by registering all the electron/photon tools with the systematics service in the algorithm and adapting the relevant part of the global trigger tool. Thanks a lot to @jmaurer for his help with this fix!