Kafka rack aware routing bug

[rukai]

I noticed a bug in rack aware routing: https://github.com/shotover/shotover-proxy/blob/4c146b8373f8a29896d118defeca1c90f4657f02/shotover/src/transforms/kafka/sink_cluster/mod.rs#L949-L952

This code path adds a node with no rack and there is no way to override that None rack later on. We need to do one of:

• not add a node here
• add a way to replace the rack later on
• immediately fetch the full node info here