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. 🤔