[BUG] Warned bots deletion after restart

[ValDesign22]

Describe the bug
It seems that restarting the API after sending inactive bot warnings, bots are deleted before the announced period.
An easy fix would be to save a timestamp/date inside a last_warned_at field to avoid this issue.

To Reproduce
Steps to reproduce the behavior:

1. Start the API
2. Wait for the inactive warnings to be sent
3. Restart the API
4. Bots are deleted

Expected behavior
Bots should be deleted only one month after and not at the restart of the app

Screenshots

Checklist

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