Backport #15895
Storing these credentials is a liability.
* Encrypt credentials with SECRET_KEY before persisting to task queue table (they need to be persisted due to the nature of the task queue)
- security in depth: helps when attacker has access to DB only, but not app.ini
* Delete all credentials (even encrypted) from the task table, once the migration is done, for safety
- security in depth: minimizes leaked data if attacker gains access to snapshot of both DB and app.ini
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