Output the stderr and stdout for ProcessInvoker.cs exception logging.

[Kykno]

I am investigating a transient failure:
microsoft/azure-pipelines-tasks#13858

It would be very much appreciated if we could possibly capture and log the node.exe std err and std out if it has data.
ProcessInvoker.cs:line 389 only logs passes some information to the exception ctor.

It would also be necessary to modify the sealed exception class:

azure-pipelines-agent/src/Agent.Sdk/ProcessInvoker.cs

Line 635 in 08a2485

public sealed class ProcessExitCodeException : Exception

Thanks!

[Kykno]

I noticed that the event subscription capability to get this information.
Also noticed that the flow from the caller (node handler) does subscribe to these event, I dont think the error I am investigating even has any stdout or stderr or it would be being logged.
Please disregard.