[Feature Request] dotnet-counters should support taking a single snapshot and exiting

The request comes from https://github.com/dotnet/docs/issues/17017

As background info we've seen several requests that are all snapshot related for different tools:
gc-dump: https://github.com/dotnet/diagnostics/pull/809
stacktraces: arg I can't find the issue but I know we've had a request to print the stack traces of all threads.
If we decide on terminology for one of these scenarios we probably want to replicate it for the others.