Cleanup outstanding user registrations

We currently have 26,014 user's with activation id's. Meaning they created an account but did not complete the confirmation process. 14,346 of these are more than a year old. I wonder if we should clean these up? Having a bunch of unused data can affect query times not to mention I think we have to pay for the space. Perhaps this could be a lambda job or something. Send them an email if they don't confirm within 30 days, at 60 days we delete their unconfirmed account.

No files, tests, or entry points are named. Start by locating the existing registration-confirmation and email workflows, then clarify the retention policy and implementation approach. Done means unconfirmed accounts receive the proposed reminders and are deleted after the stated time limits without affecting confirmed users.

Written by the indexing model from the issue text.