Add an easy way to measure time spent in layers

[bart-degreed]

We have PerformanceReports to run load tests and verify scalability, but these are black-box tests. On the other end of the spectrum, we have benchmarks using BenchmarkDotNet to measure the performance and allocations of a small piece of code.

What we don't have is an easy way to see how much time is spent (relatively and absolutely) inside the various layers (controllers, services, repositories, serialization, etc) of JADNC. It would enable us to identify code paths worth considering for optimization. And seeing the overall performance impact on changes like switching from Newtonsoft.Json to System.Text.Json.