Add RTA/2023.07.16 stack

Checkpoint release. The more important MRs are listed under https://gitlab.cern.ch/groups/lhcb/-/milestones/6#tab-merge-requests . Complete lists in the release notes.

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