Draft: Adding access to electron SFs via CorrectionLib

I'm implementing electron ID SF for our analysis and I thought it'd be useful to have the functionality to calculate electron ID SF in CMGRDF.

I've tried as much as possible to use RVec operations instead of having a standard loop per object. Not sure if that gives a performance benefit, but it felt like the right thing to do.

Due to timeline reasons, cannot implement Photon ID SF at the moment, but the interface should be rather similar. Photon has different possibilities to choose from (like muons), so I'd follow that interface.

I will add a unit test in the near future, so keeping as draft for now.