[WIP][SPARK-3797] Run external shuffle service in Yarn NM

This creates a new module `network/yarn` that depends on `network/shuffle` recently created in #3001. This PR introduces a custom Yarn auxiliary service that runs the external shuffle service. As of the changes here this shuffle service is required for using dynamic allocation with Spark.

This is still WIP mainly because it doesn't handle security yet. I have tested this on a stable Yarn cluster.
"spark.test.dynamicAllocation" might be a name more in line with other test-only properties. Also please add some documentation or name that indicates what it means to be testing.