Add Grafana datasource/plugin info

[lukekim]

• Infinity works well with Spice: https://grafana.com/grafana/plugins/yesoreyeram-infinity-datasource
• Info on Spice.ai Plugin: https://grafana.com/grafana/plugins/spiceai-spicexyz-datasource/

[claudespice]

Triage notes (state as of 2026-04):

Current docs: website/docs/monitoring/grafana/index.md covers monitoring Spice with Grafana via Prometheus scrape and the prebuilt dashboard. It does not cover using Spice as a data source in Grafana panels — which is what the two plugin links in this issue are about.

Plugin verification:

• ✅ Infinity datasource — still actively maintained (now by Grafana Labs, current version 3.8.0). Pointer still valid for "query Spice HTTP API from Grafana panels."
• ⚠️ Spice.ai datasource plugin — page now shows "the commercial agreement for this plugin has expired." Latest version is 0.0.4 and the description references the legacy Spice.ai "web3 data provider" product, not the current OSS runtime / Cloud Platform. Linking to it from the current docs would point readers at an effectively deprecated artifact.

Suggested scope, if revisiting:

A new section on monitoring/grafana/index.md (or a parallel "Use Spice as a Grafana data source" page) covering the Infinity datasource path against Spice's HTTP / Flight SQL endpoints. The legacy spiceai-spicexyz-datasource plugin should not be referenced unless it's been republished against the current product surface.

Leaving open and assigned for @ewgenius's call on whether to take it forward at the reduced scope.