feat: supports validate nested DTO ✨

[zhaoyiming0803]

Supports validate nested DTO:

import {
  IsString,
  IsNotEmpty,
  ValidateNested,
  IsNotEmptyObject,
} from 'class-validator';

class Args1 {
  // Each dto field must have a class validator 
  name: string;
}
export class CreateCityDto {
  @IsNotEmptyObject()
  @ValidateNested()
  args2: Args2;

  @IsNotEmptyObject()
  @ValidateNested()
  args1: Args1;
}

export class Args2 {
  // Each dto field must have a class validator 
  name: string;

  @ValidateNested()
  args3: Args3
}
 
class Args3 {
  // Each dto field must have a class validator
  name: string
  
  // There must be at least 2 class validators for a dto item with IsOptional
  @IsOptional()
  message: string
}