Use concurrency information from SDK Harness in Flink Portable Runner

[kennknowles]

Based on the discussion https://lists.apache.org/thread.html/0cbf73d696e0d3a5bb8e93618ac9d6bb81daecf2c9c8e11ee220c8ae@%3Cdev.beam.apache.org%3E

Use SDK Harness concurrency information in Flink runner to schedule bundles.

Imported from Jira BEAM-5167. Original Jira may contain additional context.
Reported by: angoenka.