Add grouping property on results

api/src/engine/models/result/result.model.ts

+import { Field, ObjectType } from '@nestjs/graphql';
+
+@ObjectType()
+export abstract class Result {
+  @Field({ nullable: true })
+  groupBy?: string;
+}

api/src/engine/models/result/table-result.model.ts

 import { Field, ObjectType } from '@nestjs/graphql';
 import { MetaData } from './common/metadata.model';
+import { Result } from './result.model';
 
 @ObjectType()
-export class TableResult {
+export class TableResult extends Result {
   @Field()
   name: string;