A solution to the capstone project at the end of [Mainmatter's telemetry workshop](https://github.com/mainmatter/rust-telemetry-workshop).
As stated in the exercise brief, this example will:
- Configure a `tracing` subscriber that exports data to both Honeycomb and stdout, in JSON format;
- Configure a suitable panic hook;
- Configure a `metric` recorder that exposes metric data at `/metrics`~~, using a different port than your API endpoints~~ (this example shows how to use the existing HTTP server);
- Add one or more middleware that:
- Create a top-level INFO span for each incoming request;
- Track the number of concurrent requests using a gauge;