ATLASRECTS-5835 : Add unit test for making sure egamma ART is not accidentally broken (in the sense of not being able to run)

This is part 1 . As adding things in the CI is the only way to guarantee to not have broken ART for now.

I will add a reference in Part 2.

Mentioning @rbielski for the later. Locally (I assume had not picked up his changes so will be tomorrow) still see

ODMerge 23:06:16 Shortened traceback (most recent user call last):
AODMerge 23:06:16   File "/cvmfs/atlas-nightlies.cern.ch/repo/sw/master_Athena_x86_64-centos7-gcc8-opt/2020-12-09T2101/Athena/22.0.23/InstallArea/x86_64-centos7-gcc8-opt/jobOptions/RecJobTransforms/skeleton.MergePool_tf.py", line 75, in <module>
AODMerge 23:06:16     include( "RecExCommon/RecExCommon_topOptions.py" )
AODMerge 23:06:16   File "/cvmfs/atlas-nightlies.cern.ch/repo/sw/master_Athena_x86_64-centos7-gcc8-opt/2020-12-09T2101/Athena/22.0.23/InstallArea/x86_64-centos7-gcc8-opt/jobOptions/RecExCommon/RecExCommon_topOptions.py", line 572, in <module>
AODMerge 23:06:16     if ConfigFlags.Trigger.EDMVersion == 3 and rec.readESD() and rec.doAOD():
AODMerge 23:06:16   File "/cvmfs/atlas-nightlies.cern.ch/repo/sw/master_Athena_x86_64-centos7-gcc8-opt/2020-12-09T2101/Athena/22.0.23/InstallArea/x86_64-centos7-gcc8-opt/python/AthenaConfiguration/AthConfigFlags.py", line 69, in __getattr__
....
AODMerge 23:06:16 RuntimeError: Input file name not set, instead _ATHENA_GENERIC_INPUTFILE_NAME_ found. Cannot read metadata.

Also @ssnyder and @amete do not know if you have any ideas to make this lighter as not sure how it will do for a debug build (it is 1 event, tracking,calo,e/gamma only but initialization takes also not trivial time ...)