Projects: Update the LCG layer and Externals version in the 24.0 branch

This MR updates the:

• LCG layer from 104d_ATLAS_1 to 104d_ATLAS_7, and
• Externals version from 2.1.9 to 2.1.10

in the 24.0 branch. Here is the full list of differences between these versions:

• LCG : https://lcginfo.cern.ch/compare_releases/None/104d_ATLAS_7/104d_ATLAS_1
• Externals : atlasexternals@2.1.9...2.1.10

The LCG layer update basically boils down to a number of generators and gperftools, while the Externals is purely technical (quote from @akraszna 😄).

Perhaps it's an overkill but let me err on the safe side and trigger a full build/tests.

Closes ATLINFR-5274.

cc: @akraszna @ewelina @elmsheus @tovsiann