PROGX-872: Add Asset family in asset response (#1123)

Author: jmleroux

content/swagger/akeneo-web-api.json

@@ -5,6 +5,10 @@ properties:
     type: string
     description: Code of the asset
     x-immutable: true
+  asset_family_code:
+    type: string
+    description: Code of the asset family
+    x-immutable: true
   values:
     type: object
     description: "Asset attributes values, see the <a href='/concepts/asset-manager.html#focus-on-the-asset-values'>Focus on the asset values</a> section for more details."