Move testnet metrics dashboard management out of the Grafana UI

metrics/README.md

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+# Metrics
+
+## Testnet Grafana Dashboard
+
+There are three versions of the testnet dashboard, corresponding to the three
+release channels:
+* https://metrics.solana.com:3000/d/testnet-edge/testnet-monitor-edge
+* https://metrics.solana.com:3000/d/testnet-beta/testnet-monitor-beta
+* https://metrics.solana.com:3000/d/testnet/testnet-monitor
+
+The dashboard for each channel is defined from the
+`metrics/testnet-monitor.json` source file in the git branch associated with
+that channel, and deployed by automation running `ci/publish-metrics-dashboard.sh`.
+
+A deploy can be triggered at any time via the `New Build` button of
+https://buildkite.com/solana-labs/publish-metrics-dashboard.
+
+### Modifying a Dashboard
+
+Dashboard updates are accomplished by modifying `metrics/testnet-monitor.json`,
+**manual edits made directly in Grafana will be overwritten**.
+
+1. Open the desired dashboard in Grafana
+2. Create a development copy of the dashboard by selecting `Save As..` in the
+   `Settings` menu for the dashboard
+3. Edit dashboard as desired
+4. Extract the JSON Model by selecting `JSON Model` in the `Settings` menu.  Copy the JSON to the clipboard
+    and paste into `metrics/testnet-monitor.json`
+5. Delete your development dashboard: `Settings` => `Delete`
+
+### Deploying a Dashboard Manually
+
+If you need to immediately deploy a dashboard using the contents of
+`metrics/testnet-monitor.json` in your local workspace,
+```
+$ export GRAFANA_API_TOKEN="an API key from https://metrics.solana.com:3000/org/apikeys"
+$ metrics/publish-metrics-dashboard.sh (edge|beta|stable)
+```
+Note that automation will eventually overwrite your manual deploy.