ATLFAST3 Configuration
Add ATLFAST3, ATLFAST3_QS, ATLFAST3MT and ATLFAST3MT_QS simulators. This merge request sweeps !39678 (merged) from 21.0 to master and in addition adds CA-based configuration for the ATLFAST3, ATLFAST3_QS, ATLFAST3MT and ATLFAST3MT_QS simulators. G4FastCaloMT is replaced by ATLFAST3MT. There is also some tidying of the SimulationSelector configuration.
There is more work to be done to get the output of the CA-based jobs to agree with the non-CA-based jobs, but this will need to happen after the reproducibility issues with ATLFAST3 have been resovled.
Edited by John Derek Chapman