[cloud][CLOUD-185] Store expiry time for organization invitations
Created by: kopancek
Description
Return consistent URL for the invitation because expiry time on the JWT is now the same as in the DB.
We also force an expiry of 7 days to all existing pending invitations with a DB migration. This way, we will never have long-lasting invitations anymore, that can be potentially misused years from now to implant organization members by a potential attacker.
Related issue
https://sourcegraph.atlassian.net/browse/CLOUD-185
Test plan
Tested with unit tests and manually