fix (related_backend): form value in sync between same backend type
fix (related_backend): form value in sync between same backend type

the attribute mapping form values would be all in sync. {...copy} and
other Object.assign({}, object) wouldn't workm only this was enough

mickael-kerjean/nuage,mickael-kerjean/nuage,mickael-kerjean/nuage,mickael-kerjean/nuage,mickael-kerjean/nuage,mickael-kerjean/nuage