Replace watchNamespaces and watchNamespaceSelector by watchNamespaceSelectors

[aslafy-z]

Deprecate watchNamespaces and encourage users to use the kubernetes.io/metadata.name label (available since 1.22) to select namespaces by name. watchNamespaceSelectors will be added to support a list of selectors instead of a single selector as watchNamespaceSelector does.

Deprecate watchNamespaces and watchNamespaceSelector and mark for removal for next major.

Originally posted by @aslafy-z in #1392 (comment)

[pepov]

As I'm thinking about it more I'm not sure I would like that API better.

As far as I understand the namespace name label was needed to allow selecting specific namespaces for network policies (where there is no other option), but in this case it seems to be an overkill and would unnecessarily complicate the API.

I just don't see the benefit here.

Reference: kubernetes/enhancements#2161

[stale]

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[pepov]

to be fair, in a new API I would consider the selector-only option