Dashboard documentation: concepts and guides

[willtsai]

What content needs to be created or modified?

With the Radius Dashboard being integrated into upcoming releases, there needs to be documentation created for accessing and using the Dashboard.

Describe the solution you'd like

Concepts and guide docs on how to make use of the Radius Dashboard

Where should the new material be placed?

• Additional content in Getting Started first app to point users to the Dashboard
• How to guide (perhaps under "Tooling"?) on navigating to and using the Dashboard portal
• Concepts to include Dashboard, either https://docs.radapp.io/concepts/why-radius/introduction/ or new concepts section altogether

The associated pull request from the Radius code repo, if applicable

Additional context

Related: https://github.com/radius-project/docs/pull/1027

AB#11068