Fix dashboards source IDs and add dashboard

[MarceloFCandido]

The previous version of the dashboards was using templated env vars for the Prometheus and Loki data sources on Grafana, which, unfortunately, aren't filled right away. Alongside that, the Node Visualizations dashboard wasn't properly added to the dashboards list.

This PR fixes both issues by:

1. hard writing generic datasource IDs so any Grafana instances can use the dashboards (this was the approach already used before);
2. adding the Node Visualization to the dashboard list on the chart values file.