feat(api): add groupBy=year to performance query DTO

Part of #6221

apps/api/src/app/portfolio/get-performance.dto.ts

@@ -1,9 +1,13 @@
 import { DateRangeFilterDto } from '@ghostfolio/api/dtos/date-range-filter.dto';
 
 import { Transform, TransformFnParams } from 'class-transformer';
-import { IsBoolean } from 'class-validator';
+import { IsBoolean, IsIn, IsOptional } from 'class-validator';
 
 export class GetPerformanceDto extends DateRangeFilterDto {
+  @IsIn(['year'])
+  @IsOptional()
+  groupBy?: 'year';
+
   @IsBoolean()
   @Transform(({ value }: TransformFnParams) => {
     return value === 'true';