Choose sizing properties for the cluster redis-cluster-cache

• Machine-type, initial shard count and node topology, resource-related redis settings.
• Replica resyncs will be more common, so we need to pay extra attention to accommodate that workload running alongside normal traffic (e.g. ensure machine-type has sufficient network throughput).

Updated conclusions: #2009 (comment 1237946792)

Initial conclusions, comparison table, and rationale: #2009 (comment 1204064541)