Fix Auto Requests crashing after client network disconnect

[parthverma1]

PR Checklist:

• I have run npm test locally and all tests are passing.
• I have added/updated tests for any new behavior.
  
• If this is a significant change, an issue has already been created where the problem / solution was discussed: [N/A, or add link to issue here]
  

PR Description

• Adds and tests idle timeout functionality for HTTP2 agent
• Adds agentIdleTimeout option to discard agent after given number of milliseconds after last use