Add support for AlmaLinux9 as 'el9'

The merge request provides the definition of the tag 'el9' for Alma Linux 9 as decided in the LIM.

NB: To run the testing, add a comment with:

Bot test PACKAGE[ PACKAGE2 ...]|all in TOOLCHAIN|all [(only|also) for LABEL-COMPILER-BUILDTYPE] please!

To ensure patches required for existing LCG branches are not lost, please add the respective labels: alsoTargeting:LCG_102-patches, alsoTargeting:master, etc.