Prepare for 97a and Gaudi v34r0

I modified the toolchain to replace the explicit list of generators version with the LCG suffix build specifically for us (in this case LHCB_2, see sft/lcgcmake!470 (merged)).

These new LCG layers, as they call them, are used to override the versions of some packages in the baseline release, so that we get a consistent and non ambiguous set of generators, so there's no need to filter from generators_versions.txt.

To make this work I had to backport from gaudi/Gaudi!1099 (merged) some CMake modules.

I also fixed some code still relying on Property (replaced ages ago in Gaudi with Gaudi::Property).

Notes: this includes the changes from !623 (closed)

CC: @bcouturi