yams #231956 don't fail on attempt to overwrite an infered relation [validation pending]

currently, when on try to add an already defined relation definition, an error is raised.

This behaviour is fine but when the relation has been infered (eg from inheritance), one may want to replace the infered relation by another.

This may in particular arise during cubicweb migration.

prioritynormal
typebug
done in0.39.1
load left0.000
closed by#d6beabec7bb3 Don't raise an error on attempt to overwrite an infered relation
patchDon't raise an error on attempt to overwrite an infered relation [applied]