Update tutorial on visualizing node metrics

[JoshOrndorff]

The grafana endpoint is being removed from Substrate in paritytech/substrate#4511 which means the tutorial for using grafana will need to be updated.

This update should not be made on pre-v2.0-3e65111 version

[Hyung-bharvest]

We are B-Harvest working on this : paritytech/substrate#4511 which allows prometheus exporter built in substrate. Our second milestone of this project is to provide easy setup grafana connected to this prometheus exporter. I expect the above linked tutorial can be updated based on our tutorial which will be provided in less than 4 weeks we expect.

We will drop additional comment here when our tutorial is ready. Thank you for raising the issue.

[JoshOrndorff]

The update has begun in #461 You're welcome to conribute there if you like @dlguddus

[nodebreaker0-0]

https://github.com/nodebreaker0-0/substrate/blob/prometheus_v0.4.0/utils/prometheus/README.md

It was written earlier, but it might be helpful for this tutorial.
In the future, we will support the entire dashboard (Mileston 2).
Setting up Prometheus is very easy, but the above address will help.

I think there should be a grafana tutorial and a prometheus tutorial at the same time.

[JoshOrndorff]

Done in #461 and #488