Make account data removal asynchronous and batched

[alexgarel]

Describe the bug

When you remove a user, there are a lot of chances that your request ends up with an error because we got a operation exceeded time limite.

This is because on user removal we must process a lot of mongodb data to change the username.

To Reproduce

Remove a user in production.

Expected behavior

We should have a nice return. The user removal should proceed safely in the background.

We can use minions to do it.
We should also do operation in batch to avoid flooding the database.

Screenshots

Additional context

Additionally it would be good to support deletion on old products.