Unmanaged replication slots being dropped by pg_auto_failover

Hello!

I am not sure if this is a bug or desired behavior, but I would like to understand it either way.

If you've manually created a replication slot on the primary (with a name not matching the pg_auto_failover slot naming convention), this slot will be dropped during a failover of the primary.

If this is not intended behavior, please see these rough steps to reproduce with [this branch](https://github.com/rheaton/pg_auto_failover/tree/issue/slot_dropping) at the bottom of [this file](https://github.com/rheaton/pg_auto_failover/blob/issue/slot_dropping/tests/slot_dropping/Makefile).

Thank you!
Rachel & @swati-nair