Draft: configuring CODEX-beta in Gauss

Changes include:

• Added "CB" to RUN3_DETECTORS list in Defaults.py.
• Added CB.pyscript implementing GetTrackerHitsAlg in the SetupExtractionImpl function and VPGaussMoni as Monitor algorithm (steps from the DD4hep hackathon slides).
• Added two test configurations to run CODEX-beta geometry in Gauss: a FixedMomentum particle gun aiming to CODEX-beta and a MomentumRange illuminating the Counting rooms.