Increase gRPC server max_worker count to default
Summary: We previously set the default max_worker count to 1 for the gRPC server. By setting this value to None, the ThreadPoolExecutor uses min(32, (os.cpu_count() or 1) + 4) max workers by default.
Test Plan: These methods and classes are already under test
Reviewers: alangenfeld, dgibson
Reviewed By: alangenfeld
Differential Revision: https://dagster.phacility.com/D6303