[Feature Request] Allow tracing configuration to stop after long GC

Perfview has a variety of GC triggers that allow the trace to stop when certain GC conditions have been met:

> [-StopOnGen2GC]
> [-StopOnGCOverMsec:0] Trigger a stop of a collect command if there is a .NET Garbage Collection (GC)
> is longer than the given number of MSec.
> [-StopOnGCSuspendOverMSec:0] Trigger a stop of a collect command if there is a .NET Garbage Collection (GC)
> where suspending for the GC took over the given number of MSec.
> [-StopOnBGCFinalPauseOverMsec:0]

The GC is requesting that support something similar for tracing on Linux. This request is coupled with the [Context Switch request](https://github.com/dotnet/diagnostics/issues/463) so wherever that one gets implemented, this one needs to be part of the same tool.

I am hoping we can find a way to do this that doesn't involve creating a bunch of highly specific command-line arguments, but I am not sure what the alternative would be offhand. If it needs to be argument spam I'm sure I can deal with it.

cc @maoni0 @sywhang @josalem