requested to merge fernando/athena:MoveFromEgammaToElectronPhotonMenu into master
This is to follow up on Egamma trigger menu tidy up. This MR is following ATR-24212. Electron specific files were moved away from Egamma folder and to Electron Folder in TriggerMenuMT. Similar for photons.
GenerateElectronChainDefs.py and GeneratePhotonChainDefs.py thought were kept in Egamma to avoid the need to modify Menu/GenerateMenuMT.py which reads these files from folder name called like the Signature (Egamma).