Externals Update, main branch (2023.12.15.)

Updated all projects to atlasexternals-2.1.7. The main changes wrt. atlasexternals-2.1.6 are (atlasexternals@2.1.6...2.1.7):

• Updated atlas_add_dictionary(...) to generate "SG::AuxTypeVectorFactoryImpl<ElementLink<T> >" dictionaries for the types in its ELEMENT_LINK argument;
  • Thanks to @ssnyder!
  • This is connected to !67758 (merged) and ATEAM-951, though it was !67758 (merged) that actually fixed an existing issue.
• Updated GeoModel to version 4.6.0;
  • Thanks to @tsulaia!
  • This is the thing that makes this MR be a draft for now, until !67858 (merged) is merged in.
• Introduced the FindSFGen.cmake module to AtlasLCG;
  • Thanks to @ewelina!
• Introduced VecMem v1.1.0 as an external, and added it to the build of AthenaExternals.

As noted in the list, this needs to go in after !67858 (merged). But much like that MR, this one also doesn't really need a cleanup of the CI nodes.

I'm setting full-integration-tests and full-unit-tests just for the dictionary code update. Everything else here is safe. (The GeoModel update is not really happening here, but rather in !67858 (merged). ) Even the dictionary update is, I'm just being overly cautious here.