It is confusing to have the plan type constants not be namespaced
by the thing they represent. We already have a namespacing
convention in place for constants, so we should use it for
Realm.plan_type as well.
This extends the invite api endpoints to handle an extra
argument, expiration duration, which states the number of
days before the invitation link expires.
For prereg users, expiration info is attached to event
object to pass it to invite queue processor in order to
create and send confirmation link.
In case of multiuse invites, confirmation links are
created directly inside do_create_multiuse_invite_link(),
For filtering valid user invites, expiration info stored in
Confirmation object is used, which is accessed by a prereg
user using reverse generic relations.
Fixes#16359.
Anders Kaseorg
Eeshan Garg
Vishnu KS
shanukun
PIG208
Tim Abbott