KIP-650 — Enhance Kafkaesque Raft semantics

Discussion KRaft

Adds pre-vote and non-leader linearizable reads to the KRaft Raft implementation so that network-partitioned leaders do not unnecessarily bump their epoch and disrupt the quorum, and so followers can serve linearizable reads without forwarding to the leader. Without pre-vote, a zombie leader that loses quorum connectivity starts a new election and increments its epoch, causing unnecessary leader churn and term inflation when connectivity is restored.

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