Add NodeState to ShotoverNode + some renaming for KafkaSinkCluster

[justinweng-instaclustr]

• Add a new ShotoverNodeState field to ShotoverNode. We are not reusing the existing NodeState for Kafka because it's possible that we will have different node states for Shotover in the future.
• Add a new configuration check_shotover_peers_delay_ms to KafkaSinkCluster which will be used when checking connection to nodes and setting node states.
• Move ShotoverNode code into a new file kafka/sink_cluster/shotover_node.rs
• Rename kafka/sink_cluster/node.rs to kafka/sink_cluster/kafka_node.rs and NodeState to KafkaNodeState

[codspeed-hq]

CodSpeed Performance Report

Merging #1758 will not alter performance

_{Comparing justinweng-instaclustr:handle-offline-shotover-nodes (f45682c) with main (25827de)}

Summary

✅ 39 untouched benchmarks

[rukai]

Looks good!