The --rpc-pubsub-enable-vote-subscription flag may be used to enable it.
The current vote subscription is problematic because it emits a
notification for *every* vote, so hundreds a second in a real cluster.
Critically it's also missing information about *who* is voting,
rendering all those notifications practically useless.
Until these two issues can be resolved, the vote subscription is not
much more than a potential DoS vector.
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