Allow restricting the Cache's ListWatch to a set of namespaces

[hasbro17]

As a follow up to #124 the manager should allow restricting the cache to a set of namespaces.

Watching on all namespaces and filtering the events(via predicates) to the desired namespaces is the only way to watch a set of namespaces currently.
The problem with that is it still requires a ClusterRoleBinding, whereas the user might want to grant more fine grained permissions of a ClusterRole with multiple RoleBindings(referring to the manager's service account).

Proposed Fix:
As discussed in #124 (comment) we can use a MultiListWatcher in the cache if the manager is passed a set of namespaces.

[DirectXMan12]

/kind feature
/priority important-longterm

[shawn-hurley]

@DirectXMan12 I think this is closed by #267

[DirectXMan12]

yep!