Function mz_storage_controller::warm_persist_state_in_background

pub(crate) fn warm_persist_state_in_background(
    client: PersistClient,
    shard_ids: impl Iterator<Item = ShardId> + Send + 'static,
) -> JoinHandle<Box<dyn Debug + Send>>

Warm up persist state for shard_ids in a background task.

With better parallelism during startup this would likely be unnecessary, but empirically we see some nice speedups with this relatively simple function.