Update customizable dashboards docs
Problem to solve
The customizable dashboards docs are completely out of date with our latest changes and the example config doesn't match our schema.
With groupoptimize looking to add a new visualization in Add VSD comparison panel as visualization for t... (#409949) it's important that the docs are updated.
Proposed solution
Update the docs to match our latest changes in the component. Add an example:
- A new dashboard configuration with panels
- A visualization configuration
And guidelines on how to add a new visualization and data source.
Follow-up
Edited by Jiaan Louw