feat: Setup initial metrics infrastructure

[CosmicHorrorDev]

This adds something that I've been wanting implemented for a while. Metrics recording and emission 🎉

There's a new section in the config file that sets the metrics recorder

[debug]
metrics = "log"
# -- or --
metrics = "tcp"

It's unset by default which uses the noop recorder (aka as cheap as it can get)

Log Recorder

(this one took a bit of work since it implements a recorder from "scratch")

When it's set to "log" the metrics start getting recorded as tracing events with some metadata attached on the span. This makes it possible to filter things pretty dynamically, and is accessible as a user doesn't need to download anything else to see the values

TCP Recorder

When it's set to "tcp" the metrics get emitted following the default metrics-exporter-tcp configuration. This means that anything that knows how to consume that can handle displaying the data live. Currently the only main program I know of is the metrics-observer binary crate, but it's unfortunately a bit limited

metrics_observer.mp4

[CosmicHorrorDev]

I think it'd be worth investigating different recorders to see if we can find more featureful ones, and document any relevant findings (including the new cfg and config stuff from this PR)