[EventHubs] Stress test embracing azure application insights for metrics/traces

[yunhaoling]

This is part 1/2 of the stress test improvement -- we could use azure applications insights + azure dashboard to better monitor our stress test running status. (part 2/2 here)

the stress test scenarios are (sync and async):

• send
• receive
• receive with checkpointstore

Metrics could include (but not limited to):

• send
  • published events count
  • error count
• receive
  • consumed events count
  • error count
• hardware
  • cpu usage
  • memory usage
• advanced
  • checkpointstoreblob call failures

Traces could include (but not limited to):

• warning/error information

Action item:

• update the current stress test code to embrace application insights
• utilize azure dash board to show the aforementioned metrics/traces