Log WARN on large batch sizes

Large batches on a coordinator can cause a lot of node stress. I propose adding a WARN log entry if batch sizes go beyond a configurable size. This will give more visibility to operators on something that can happen on the developer side.

New yaml setting with 5k default.

# Log WARN on any batch size exceeding this value. 5k by default.
# Caution should be taken on increasing the size of this threshold as it can lead to node instability.

batch_size_warn_threshold: 5k