Update Grafana dashboard in Monitor node page

[Imod7]

Description

Updated the Grafana dashboard used in the "Installing Grafana" section of the "Monitor your node" wiki page.

Issue

The reason of this update is that I tried to use the My Polkadot Metrics dashboard but most of the metrics are outdated so I do not get any data on the dashboard.

Some examples of outdated metrics are the following (while syncing the Polkadot chain with ./target/release/polkadot --chain polkadot --prometheus-external) :

• all the metrics in the "My Polkadot Metrics" dashboard are prefixed with polkadot while the node exposes metrics with the prefix substrate, e.g.:
  • metric in dashboard polkadot_tasks_polling_started_total -> metric exposed from node substrate_tasks_polling_started_total
  • polkadot_sub_libp2p_peers_count -> substrate_sub_libp2p_peers_count
• some metrics like polkadot_load_avg, polkadot_cpu_usage_percentage or polkadot_memory_usage_bytes are not found under the list of metrics that the node exposes (http://localhost:9615/metrics). Even when I change the prefix from polkadot to substrate.

Proposed Solution

Use the dashboard Substrate Node Metrics which is an updated version of the "My Polkadot Metrics" dashboard wtih some extra panels. When imported it will show data like in the screenshot below:

[CrackTheCode016]

This LGTM, thank you for catching this!

Many of our Maintain docs probably need a rehaul..