Main purpose of this MR: Change of full_menu test to run from TriggerMenuMT and subsequently also the slice_XXX (XXX= signature tests) (ATR-19845)

Changes made:
* Copied full_menu test to full_menu_cf test (for the build variant), including .py, .ref, .sh files
* Modified full_menu test to run from TriggerMenuMT
* Note: for now no Bphysics chains enabled, slight modifications of chains but constant counts for those chains that were enabled before in the same configuration
* Also Note: Electron and Photon tests now run the same configuration of EGAMMA chains (not separate anymore due to the way flags were set up historically); TriggerFlags might need to be reworked but this will happen at a later time.
* Modified testHLT_MT.py and full_menu.py to set the TriggerFlags for the menu generation
* Fix of flake8 errors in HLTCFDot.py and MenuComponents.py