cubicweb #4846892 use foreign keys for relations [validation pending]

we have a few bugs where we insert relations for eids that are not (or not anymore) in the entities table. using foreign keys would prevent that from happening.

prioritynormal
typeenhancement
done in3.21.0
load1.000
load left0.000
closed by#aaabcb64f77f Use foreign keys for relations tables
patch[migration/3.21] Add missing foreign keys when upgrading [applied]Use a moved_entities table to record external entities moved to the system source [applied][server] change order of entities table modification vs entity creation/deletion [applied]Ask sqlite to check foreign keys [applied]Add reference from etype table's eid column to the entities table [applied]Use foreign keys for relations tables [applied]Add foreign key for inline relations [applied]Use our version of schema2sql [applied]Steal schema2sql module from yams [applied]Add missing foreign keys when upgrading [rejected]