Please provide a method to shutdown thread pool used in com.sendgrid.BaseInterface.attempt

[taksatou]

Issue Summary

Please provide a method to shutdown thread pool used in com.sendgrid.BaseInterface.attempt.
Even after com.sendgrid.SendGrid instance is discarded, the thread pool is still alive and it prevents the JVM process from exiting.

Steps to Reproduce

Just call com.sendgrid.BaseInterface.attempt, and then, the JVM process won't exit.

Technical details:

• sendgrid-java version: 4.7.6
• java version: openjdk version "16.0.2" 2021-07-20

[jackcviers]

Agreed it should implement AutoCloseable. The close method can use awaitTermination while catching the InterruptedException to implement the close method, just like in the example under ExecutorService.