Sweeping !25081 from 21.0 to master. Add SimulateCavern simFlag, which can be used independently of CavernBG and cosmics simulation

Add SimulateCavern simFlag, which can be used independently of CavernBG and cosmics simulation

See merge request !25081 (merged)

added sweep:from 21.0 label

Adding original author @jchapman as watcher.

This merge request affects 5 packages:

• Simulation/G4Atlas/G4AtlasApps
• Simulation/G4Atlas/G4AtlasServices
• Simulation/G4Atlas/G4AtlasTools
• Simulation/ISF/ISF_Config
• Simulation/ISF/ISF_Geant4/ISF_Geant4Tools

Adding @jchapman ,@vpascuzz as watchers

added Simulation master review-pending-level-1 labels

CI Result SUCCESS

	Athena	AthSimulation
externals
cmake
make
required tests
optional tests

Full details available at NICOS MR-25110-2019-07-25-06-42
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 1443]

added review-approved label and removed review-pending-level-1 label

merged

mentioned in commit 612d0c4c

added sweep:ignore label