Add cluster-wide EventBus

[mcanevet]

Is your feature request related to a problem? Please describe.
We are currently using a single Kafka as event bus. We have to define the same default EventBus resource in all our Namespaces where we are using ArgoEvents, with a Secret to store the credentials, which is not convenient.

Describe the solution you'd like
I'd like to have a ClusterEventBus resource that I, as platform administrator, could deploy for all my users, that they could refer is their EventSource and Sensor resources.

Describe alternatives you've considered
I currently use a Kyverno ClusterPolicy to clone a reference Secret and EventBus resources in all Namespaces.

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