Modification to allow xAODDecaysFinalStateFilter

Description of bug

While running tests with 23.6.26, errors from the xAODDecaysFinalStateFilter were found. Essentialy the complaint was about a missing container: AADecayFilter ERROR No TruthParticle collection with name TruthGen found in StoreGate

Changes introduced

This line was added:

createxAODSlimmedContainer("TruthGen",prefiltSeq)prefiltSeq.xAODCnv.AODContainerName = 'GEN_EVENT'

Tests

Athena 23.6.28 release was used and mc23 production will be requested.

Issues resolved

See JIRA-11087

Closes #