[consolidated] Update channel's status.subscribers based on the dispatcher propagated consumer readiness

[devguyio]

Problem
The solution that was proposed in #182 did not fix the problem of adding the subscriptions to the channel only when the corresponding consumer in the dispatcher is ready and due to a lag in Sarama between the consumer group creation and starting the consumer, it seems there's no other way than to propagate the consumer readiness from the dispatcher

Exit Criteria
A measurable (binary) test that would indicate that the problem has been resolved.

Time Estimate (optional):
3d

Additional context (optional)
#134
#98
knative/eventing-contrib#1556
#182

[github-actions]

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[devguyio]

Fixed by #433