The secretName parameter was being used as a literal secret name
'CORE_SECRET' which doesn't exist. This caused harbor-core pods to
fail mounting volumes.
The correct approach is to use existingSecret for credential keys,
and let Harbor manage its own internal secrets.
Harbor Helm chart expects 'secret' key not 'CORE_SECRET' for the
CORE_SECRET environment variable. This was causing jobservice pod
to fail with CreateContainerConfigError.
Fixes: harbor-jobservice-757bbf44cc-tvznq error