Benchmarks for attachStacktrace =true

Whenever possible we'd like to opt-in to features so users get the value without having to be aware or make a decision.

`AttachStacktrace`=true would be such a feature. The trade off here is the overhead added to folks that use Sentry as a logging too (sending many events per second from a single process).

There was a [unconfirmed report of performance degradation that could have been caused by the use of `attachStacktrace`.](https://github.com/getsentry/sentry-dotnet/issues/479)

It's likely the right choice for Client based apps (UWP, WPF, Xamarin, etc) but not for ASP.NET.

We need some benchmarks to have a better idea of the cost of getting these stacktraces for normal `CaptureMessage` calls.

With that information we can [decided whether to enabled it by default](https://github.com/getsentry/sentry-docs/pull/2815#issuecomment-753719123).