Release Gauss v55r4

A new release for Sim10 with new major features, and moving to latest Gaudi and LHCb release. It also moves to LCG_101. It brings along new Run2Support v2r1 release.

Release checklist (to be filled by the shifter)

• release build validation (to be checked with the MR author)
• RPMs deployment
• CVMFS installation
• web pages update

Due to issues with with LHCB_7 in Gauss and LCG_vanilla in the used project, the OPT variable need to be set as described in the Note in the documentation