KIP-624 — Consolidate Offset Validation into Fetch Protocol

Discussion ProtocolBroker

Proposes making the `OffsetForLeaderEpoch` validation step optional (skippable) during follower log truncation so that followers that are already in sync can skip the round-trip to the leader. The `OffsetForLeaderEpoch` RPC is sent unconditionally on follower startup even when the follower's epoch already matches the leader, adding unnecessary latency to the catch-up path.

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