title: TypeORM using SoftRemove and Unique decorator
body: <p>Help me please resolve next issue. I use NestJS + TypeORM softRemove/softDelete for delete records. And I want to apply @Unique decorator only for undeleted records.
  My remove method like:</p>
  <pre><code>public async delete(id: number): Promise&lt;UpdateResult&gt; {
     return await this.repo.softDelete(id);
  }
  </code></pre>
  <p>In Entity will be perfect something like:</p>
  <pre><code>@Entity('role')
  @Unique('UQ_TITLE', ['title', 'deletedDate IS NULL'])//IS NULL not supported there :(
  export class Role {
  
      @Column({ type: 'varchar', nullable: false })//may be exists some expression for column settings
      title: string;
  
      @DeleteDateColumn({ select: false })
      deletedDate?: Date;
  }
  </code></pre>