Feature request: Read CronJob secrets from different namespace than the cluster's

The CronJobEnvironmentSecretVariables are being read from the cluster namespace by default: https://github.com/zalando/postgres-operator/blob/master/pkg/cluster/k8sres.go#L1205

Should it be possible to define a namespace override for this secret, to prevent secret duplication if multiple clusters to multiple namespace haven been deployed?

Proposal:

type LogicalBackup struct {
	LogicalBackupCronjobEnvironmentSecret     string `name:"logical_backup_cronjob_environment_secret" default:""`
	LogicalBackupCronjobEnvironmentSecretNamespace     string `name:"logical_backup_cronjob_environment_secret_namespace" default:""`
}

func (c *Cluster) getCronjobEnvironmentSecretVariables() ([]v1.EnvVar, error) {
// [..]
	var secretNamespace string

	if c.OpConfig.LogicalBackupCronjobEnvironmentSecretNamespace == "" {
		secretNamespace = c.OpConfig.LogicalBackupCronjobEnvironmentSecretNamespace
	} else {
		secretNamespace = c.Namespace
	}
	
	secret, err := c.KubeClient.Secrets(secretNamespace).Get(

Start in pkg/cluster/k8sres.go around the getCronjobEnvironmentSecretVariables implementation at line 1205, then locate the LogicalBackup configuration definition. Add support for an optional secret namespace override while preserving the cluster namespace default, and verify that CronJobs read the environment secret from the selected namespace.