Exclude namespaces from being managed by operator

[1davidmichael]

We have a case where we have ECK running in a cluster and would like to use it to manage a cluster in a given namespace. But we also would like to have another operator that manages all other Elastic resources.

For example: prod namespace resource are managed by one operator.

Other ephemeral environments are managed by a separate operator and the namespaces of these are generated and change over time. As a result we can't use the managedNamespaces to pin to specific namespaces. To accomplish this it would be really nice to have something like ignoredNamespaces so we can use one operator to manage that ignored namespace and a separate operator to manage all the others.