cubicweb-elasticsearch #17079908 ES document id should be customizable [validation pending]

For now, es document id is the entity eid. This is a sane default behaviour but one should be able to use any other attribute (another unique attribute for instance)

prioritynormal
typeenhancement
done in0.6.0
load0.250
load left0.000
closed by#7859ebfada15 allow overriding of ES id attribute
patchallow overriding of ES id attribute [applied]