[Streams] Fix StreamRefSettings.FinalTerminationSignalDeadline never initialized

[Arkatufus]

The FinalTerminationSignalDeadline property of StreamRefSettings never get initialized from HOCON settings, it is always TimeSpan.Zero.

Changes

• Make sure FinalTerminationSignalDeadline is initialized.
• Clean up reference.conf, convert all tabs to spaces

[Aaronontheweb]

@Arkatufus is this setting actually used anywhere currently?

[Arkatufus]

Its being used here:

akka.net/src/core/Akka.Streams/Implementation/StreamRef/SourceRefImpl.cs

Lines 250 to 258 in cc9435c

	case Terminated terminated:
	if (Equals(_partnerRef, terminated.ActorRef))
	// we need to start a delayed shutdown in case we were network partitioned and the final signal complete/fail
	// will never reach us; so after the given timeout we need to forcefully terminate this side of the stream ref
	// the other (sending) side terminates by default once it gets a Terminated signal so no special handling is needed there.
	ScheduleOnce(TerminationDeadlineTimerKey, Settings.FinalTerminationSignalDeadline);
	else
	FailStage(new RemoteStreamRefActorTerminatedException(
	$"Received UNEXPECTED Terminated({terminated.ActorRef}) message! This actor was NOT our trusted remote partner, which was: {_partnerRef}. Tearing down."));

Its also used as a stream attribute, though the attribute isn't being used anywhere:

akka.net/src/core/Akka.Streams/Attributes.cs

Lines 927 to 931 in cc9435c

	/// <summary>
	/// The time between the Terminated signal being received and when the local SourceRef determines to fail itself
	/// </summary>
	public static Attributes CreateFinalTerminationSignalDeadline(TimeSpan timeout)
	=> new(new FinalTerminationSignalDeadline(timeout));