Specify the size of the thread pool for the executor used to execute
callbacks of CompletableFutures of async Table operations. By default, these
futures are completed (called) by the threads of the native store client. Depending
on the implementation of the native client, it may or may not allow executing long
running operations in the callbacks. This config can be used to execute the callbacks
from a separate executor to decouple from the native client. If configured, this
thread pool is shared by all read and write operations.