[Refactor] Update user short link relation in Usecase

[arberiii]

What is frustrating you?
When updating the alias of a short link, the relation of user short link is updated only because they are joint in postgres database but it is not updated in updater usecase

short/backend/app/usecase/shortlink/updater.go

Lines 80 to 81 in b945aac

	return u.shortLinkRepo.UpdateShortLink(oldAlias, shortLink)
	}

Your solution
Update user short link relation in Usecase

[magicoder10]

Huh, good question. Not sure whether we have to manually do this.

[arberiii]

A more detailed dissucion in issue #958.