BUG/ENHANCEMENT: Ensure existing members of a level that auto-adds Affiliates get created

[kimcoleman]

Describe the bug
There’s a post on our site about Creating Affiliate Codes for Existing Users.

We should consider either logic to use Action Scheduler that repairs missing people when that setting changes OR logic so that as users log in, their affiliate status is repaired.

To Reproduce
Steps to reproduce the behavior:

1. Have a site with existing levels and members of those levels.
2. Edit a level and check the box to "Automatically create affiliate code".
3. See that existing members of this level are not affiliates.
4. See that new members that join the level become added as affiliates.
   If applicable, please attach a screenshot to make your issue clearer.