TMDM-7242: "Can't create records in Staging when Entity Primary Key is Composite-Key..."

Fixes issue when staging storage underlying storage is not a hibernate storate (can be a cache storage implementation).
Fixes issue leading to incorrect mapping of FK fields in flat mapping strategy (due to a change in TMDM-7615)
(https://jira.talendforge.org/browse/TMDM-7242)
(https://jira.talendforge.org/browse/TMDM-7615)
Merge branch 'maintenance/5.6'