dotnet-gcdump should trigger warning if the heap size is huge

Triggering a GC dump on a process with a huge heap (i.e. hundreds of GB) can potentially kill the service for minutes because it forces a full GC on the target process. We should probably show some warning message in case dotnet-gcdump is about to kill the target process by doing this.

An even better solution would be to see the GC heap size of the target app (prob. through EventCounter?) and then if it's above certain threshold, display the warning message and make sure the user knows what this is going to do to the target application.