feat: support multiple namespaces and namespace label selector filtering

[Dasmat13]

Resolves #3565

Description

This PR introduces support for watching multiple namespaces and namespace label filtering for Service and Ingress sources.

Changes

• Multiple Namespaces: Allows --namespace to accept a comma-separated list of namespaces.
• Namespace Label Filter: Adds a new --namespace-label-filter flag to dynamically filter namespaces based on a label selector.
• Dynamic Watch Scope: Automatically adjusts the informer namespace watch scope.
• Event Throttling: Drops irrelevant namespace events to prevent unnecessary reconciliations.
• Tests: Full unit test coverage included.

[kubernetes-prow]

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[kubernetes-prow]

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[Dasmat13]

Hi @u-kai and @vflaux 👋

When you have a chance, could you please take a look at this PR? It also needs /ok-to-test before the required CI jobs can run.

The implementation adds support for watching multiple namespaces and namespace label selectors while keeping the existing single-namespace behavior intact. Happy to make any changes based on your feedback. Thanks!