feat(Relation3TiersController): add setGrandChildList method

solidify-controller/src/main/java/ch/unige/solidify/controller/Relation3TiersController.java

@@ -358,6 +358,16 @@ public abstract class Relation3TiersController<T extends Resource, V extends Res
     }
   }
 
+  public HttpEntity<HttpStatus> setGrandChildList(@PathVariable String parentid, @PathVariable String id, @RequestBody String[] gdChildIds) {
+    try {
+      this.delete(parentid, id, null);
+    } catch(SolidifyHttpErrorException e) {
+      // No-op
+    }
+    this.create(parentid, id, gdChildIds);
+    return new HttpEntity<>(HttpStatus.OK);
+  }
+
   /**
    * Update all relations between the parent and the child, with given relation properties
    *