HTTP/2 Code is Refactored

The HTTP/2 Agent code is refactored from  versions 8.1.9, 8.2, and 10.6.

As a result of this, MZ-35843 "Thread Leak in HTTP/2 Client Agent" is resolved, where the internal cache caused the HTTP/2 Client Agent to leak threads when a workflow had stopped, since not all underlying 3pp threads were stopped. As a result you needed to restart the EC that the workflow was running on to release the threads. This is no longer necessary.