Add docker compose metrics setup

[KolbyML]

Tyler wanted a way to easily setup prometheus/grafana locally. Here is my setup using docker compose.

Quick run instructions

./target/bin/nitro --dev --metrics --metrics-server.addr=0.0.0.0

^ enable metrics on nitro node use --metrics-server.addr=0.0.0.0 for maximum cross platform compatibility (change to local host at your own risk 👻)

cd metrics
docker compose up

^ cd into the metrics folder, then run docker compose up to start the prometheus/grafana setup

View your grafana dashboard at http://localhost:3000/ username/password is admin

For more information read the readme at metrics/README.md

Intentions

This PR is just to add my grafana setup to this repo as suggested by Tsahi and to help Tyler. Deeper integrations into the nitro-testnode can happen in future PR's if desired. I want this metrics setup to be compatible with running nitro locally regardless though ideally. As I want to use this setup if I am running nitro locally or https://github.com/OffchainLabs/nitro-devnode

[relyt29]

I'm not tsahee so wait for approval from him, but I can confirm that I reviewed the code and I don't have any issues with it, and I was also able to reproduce the desired result by following instructions and running nitro locally with metrics

Thanks @KolbyML! :)