When seaweedfs/raft elects a new leader, transfer hashicorp raft leadership
to the same node. This ensures both raft systems always have the same leader,
allowing dual-write to work correctly.
Changes:
- Add SyncHashicorpRaftLeadership() to transfer hashicorp raft leadership
- Call sync on seaweedfs/raft leader change event
- Only the current hashicorp raft leader can initiate transfer
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