The core API will be started before the cluster is started in order to
access the cluster endpoints during a cluster upgrade. If TLS is enabled,
possibly stale certificates are loaded into the cache. Otherwise the
leader has to be contacted via the cluster API which might have changed.
This secret will be used to encrypt automatically obtained secrets at
rest, i.e. in a storage. They will be decrypted on demand. If the
secret is wrong, stored certificates can't be decrypted. For changing
the secret, the stored certificated must be deleted first in order
to obtain new ones that will be encrypted with the new secret.
