[8.0] fix: Singularity issue with non existing SE + JobAgent issue with exception raised during submission

[aldbr]

I found this double issue while playing with the Site configuration:

• Initial issue:

2025-04-03T15:36:40,991592Z WorkloadManagement/JobAgent/Singularity INFO: Creating singularity container
2025-04-03T15:36:40,992786Z WorkloadManagement/JobAgent/WorkloadManagement/JobAgent INFO: Found Job LogLevel JDL parameter with value DEBUG

# The issue that triggers the first problem: a SE section is not found
2025-04-03T15:36:41,618254Z WorkloadManagement/JobAgent ERROR: StorageFactory._getConfigStorageName: Failed to get storage options Path /Resources/StorageElements/<NOT_EXISTING_SE> does not exist or it's not a section

• 1st problem: self.storages is not initialized because the StorageElement object is malformed (SE section not found)

2025-04-03T15:36:41,619437Z WorkloadManagement/JobAgent/WorkloadManagement/JobAgent ERROR: Exception occurred when submitting JobID: 2140558
Traceback (most recent call last):
  File "/cvmfs/lhcbdev.cern.ch/lhcbdirac/versions/v12.0.0a11-1743438349/Linux-aarch64/lib/python3.11/site-packages/DIRAC/WorkloadManagementSystem/Agent/JobAgent.py", line 637, in _submitJob
    result = self.computingElement.submitJob(
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/cvmfs/lhcbdev.cern.ch/lhcbdirac/versions/v12.0.0a11-1743438349/Linux-aarch64/lib/python3.11/site-packages/DIRAC/Resources/Computing/SingularityComputingElement.py", line 384, in submitJob
    mountedPath = StorageElement(seName).getStorageParameters(protocol="file")["Value"]["Path"]
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/cvmfs/lhcbdev.cern.ch/lhcbdirac/versions/v12.0.0a11-1743438349/Linux-aarch64/lib/python3.11/site-packages/DIRAC/Resources/Storage/StorageElement.py", line 705, in getStorageParameters
    for storage in self.storages.values():
                   ^^^^^^^^^^^^^
  File "/cvmfs/lhcbdev.cern.ch/lhcbdirac/versions/v12.0.0a11-1743438349/Linux-aarch64/lib/python3.11/site-packages/DIRAC/Resources/Storage/StorageElement.py", line 1368, in __getattr__
    raise AttributeError(f"StorageElement does not have a method '{name}'")
AttributeError: StorageElement does not have a method 'storages'
2025-04-03T15:36:41,620682Z WorkloadManagement/JobAgent/WorkloadManagement/JobAgent ERROR: Job submission failed 2140558

• 2nd problem: instead of capturing the message of the exception to reschedule the job, we capture the exception itself

2025-04-03T15:36:41,620789Z WorkloadManagement/JobAgent/WorkloadManagement/JobAgent ERROR: Error in DIRAC JobWrapper or inner CE execution: StorageElement does not have a method 'storages'
2025-04-03T15:36:41,620842Z WorkloadManagement/JobAgent/WorkloadManagement/JobAgent WARN: Failure ==> rescheduling (during StorageElement does not have a method 'storages')
2025-04-03T15:36:41,620910Z WorkloadManagement/JobAgent/WorkloadManagement/JobAgent ERROR: Agent exception while calling method <bound method JobAgent.execute of <DIRAC.WorkloadManagementSystem.Agent.JobAgent.JobAgent object at 0x40000e892f10>>
Traceback (most recent call last):
  File "/cvmfs/lhcbdev.cern.ch/lhcbdirac/versions/v12.0.0a11-1743438349/Linux-aarch64/lib/python3.11/site-packages/DIRAC/Core/Base/AgentModule.py", line 314, in am_secureCall
    result = functor(*args)
             ^^^^^^^^^^^^^^
  File "/cvmfs/lhcbdev.cern.ch/lhcbdirac/versions/v12.0.0a11-1743438349/Linux-aarch64/lib/python3.11/site-packages/DIRAC/WorkloadManagementSystem/Agent/JobAgent.py", line 311, in execute
    result = self._checkSubmittedJobs()
             ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/cvmfs/lhcbdev.cern.ch/lhcbdirac/versions/v12.0.0a11-1743438349/Linux-aarch64/lib/python3.11/site-packages/DIRAC/WorkloadManagementSystem/Agent/JobAgent.py", line 700, in _checkSubmittedJobs
    self._rescheduleFailedJob(jobID, result["Message"])
  File "/cvmfs/lhcbdev.cern.ch/lhcbdirac/versions/v12.0.0a11-1743438349/Linux-aarch64/lib/python3.11/site-packages/DIRAC/WorkloadManagementSystem/Agent/JobAgent.py", line 828, in _rescheduleFailedJob
    self.jobs[jobID]["JobReport"].setJobStatus(
  File "/cvmfs/lhcbdev.cern.ch/lhcbdirac/versions/v12.0.0a11-1743438349/Linux-aarch64/lib/python3.11/site-packages/DIRAC/WorkloadManagementSystem/Client/JobReport.py", line 38, in

BEGINRELEASENOTES
*Resources
FIX: do not try to use a malformed StorageElement instance in SingularityCE
*WorkloadManagement
FIX: report the message of the Exception instead of the Exception itself in JobAgent.submitJob
ENDRELEASENOTES

[DIRACGridBot]

Sweep summary

Sweep ran in https://github.com/DIRACGrid/DIRAC/actions/runs/14305428060

Successful:

• integration