cubicweb-vcsfile #4819618 migration path for repos with path and no source_url [validation pending]

we should not just drop the path

priorityimportant
typebug
done in2.0.1
load0.500
load left0.000
closed by#89dae0f20763 Migrate from path to source_url on upgrade (closes #4819618)
patchMigrate from path to source_url on upgrade (closes #4819618) [applied]