remove hasPaid property from the user

[vincanger]

because we have subscriptionStatus, hasPaid seems to be largely redundant. if user.subscriptionStatus === undefined this would be the same as hasPaid === false.

• remove hasPaid
• check to make sure code works with users with credits but without a subscrptionTier
• update relavant docs https://docs.opensaas.sh/general/user-overview/#stripe-and-subscriptions