Add benchmarks that test the scalability of large requests and large responses

[davidfowl]

ASP.NET uses a buffer to disk then write to request/response in a couple of scenarios:

• Buffering the request body (via explicit calls to to EnableBuffering)
• Buffering multipart files
• Buffering the response body for JSON.NET based formatting and XmlSerializer based formatting

Our defaults today were picked without any measurements, we should measure how throughput and memory as we add more concurrency for these large read and write scenarios where data is spooled to disk.

Related:

• https://github.com/dotnet/aspnetcore/issues/17843
• https://github.com/dotnet/aspnetcore/issues/21187

cc @Tratcher @pranavkm @rynowak