[dotnet-dump] Allow collect to start the proccess itself.

Right now you have to pass in the pid of the process to `dotnet-dump collect` so its a manual process and problematic when trying to diagnose a startup issue.

In my specific use case I was trying to debug a stack overflow exception and it was really complicated to start the app and figure out the pid in time before the app crashed.

It would be nice if one could simply do `dotnet-dump collect -- start command args` and have the tool start the process and the collection right away.