The status manager channel forces all container status to be
processed, even if multiple updates are generated in succession.
Instead of queueing the updates, just remember which ones changed
and process them in a batch. This should reduce QPS load from
the Kubelet for status, reduce latency of status propagation to
the API in general, and is easier to reason about.
This also prevents status from being lost when the channel is
full - all updates sent by SetPodStatus are guaranteed to be
recorded. Changing to remove the channel allows us to set a
marker flag when the pod worker state machine completes that
avoids the status manager having to call into the pod worker
directly.
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