Comment 0 for bug 2061314

It seems that since separate CA certs ware added for etcd and front proxy in https://review.opendev.org/c/openstack/magnum/+/746864, the cleanup code to remove these certificates was never put in place, as can be seen here: https://opendev.org/openstack/magnum/src/branch/master/magnum/conductor/handlers/common/cert_manager.py#L240

Steps to reproduce:
Create a Magnum cluster and then delete it. Inspect the Barbican database to see that two certificates, along with their private keys and passphrases are still left:

$ mysql barbican -t <<<"select name, status, created_at, deleted_at from secrets order by created_at desc limit 12;"
+------------------------+--------+---------------------+---------------------+
| name | status | created_at | deleted_at |
+------------------------+--------+---------------------+---------------------+
| Private Key Passphrase | ACTIVE | 2024-04-14 18:32:48 | 2024-04-14 19:06:39 |
| Certificate | ACTIVE | 2024-04-14 18:32:48 | 2024-04-14 19:06:39 |
| Private Key | ACTIVE | 2024-04-14 18:32:48 | 2024-04-14 19:06:39 |
| Private Key | ACTIVE | 2024-04-14 18:32:47 | NULL |
| Private Key Passphrase | ACTIVE | 2024-04-14 18:32:47 | NULL |
| Certificate | ACTIVE | 2024-04-14 18:32:47 | NULL |
| Private Key Passphrase | ACTIVE | 2024-04-14 18:32:46 | NULL |
| Private Key | ACTIVE | 2024-04-14 18:32:46 | NULL |
| Certificate | ACTIVE | 2024-04-14 18:32:45 | NULL |
| Private Key Passphrase | ACTIVE | 2024-04-14 18:32:44 | 2024-04-14 19:06:38 |
| Private Key | ACTIVE | 2024-04-14 18:32:44 | 2024-04-14 19:06:38 |
| Certificate | ACTIVE | 2024-04-14 18:32:43 | 2024-04-14 19:06:38 |
+------------------------+--------+---------------------+---------------------+

Expected result:
All created certificates should be removed when the cluster is deleted.