support alternate unique keys

[uladkasach]

for example:

• short url is unique by slug as well as separately by forUrl

  export class ShortUrl extends DomainValueObject<ShortUrl> implements ShortUrl {
  public static schema = schema;
  public static unique = [['slug'], ['forUrl']];
  }

• sms is unique by externalId as well as separately by apiMessageId

  export class Sms extends DomainEntity<Sms> implements Sms {
  public static schema = schema;
  public static unique = [['externalId'], ['apiMessageId']];
  public static updatable = ['status'];
  }

[uladkasach]

may want to make the exposed dao method:

findByUnique(args: { slug: string } | { forUrl: string }) => { ... }

so that its clear its unique on both - and to continue the expectation that each domain object can be "foundByUnique"

[uladkasach]

another example:

export class Lot extends DomainEntity<Lot> implements Lot {
  public static unique = [
    ['requestUuid'], // ensures retried client requests do not result in more than one lot (since lotNumber is generated inside of the service)
    ['auctionUuid', 'lotNumber'] // ensures a lot number is used max once per auction
  ];
}