Draft: First version of RICH simulation: GaussPhotonics package based on Gaussino and DD4HEP

This is a first version of the new GaussPhotonics package based on Gaussino and DD4HEP, for RICH simulation. So far it runs with a version of Gaussino which is a few months old. It creates G4Hits; however they are not yet copied to MCHit structure. An example of the options file used for running this with particle gun is attached. GaussPhotonics-example-GaussoptionsFile.py.txt. The pgun options are in some files in Gauss/Gen/LbPGuns/options area. However they seem to be needed in the corresponding Gaussino area. In this case an MR will be made for them in Gaussino package also. Work in progress to run with recent versions of Gaussino. This needs a version of the 'Detector' package that is at least a 'recent master version'; a better option is a 'master version' that is expected to be available in a few days.
For reference, a log file obtained when running Gauss for a few events is attached. Gauss-run-example.log . This draft MR is made following a recent suggestion from @mimazure .