chore: Generate dashboard configmap from separate json files

[ArthurSens]

While doing the release for v2.52, I wanted to extend the prombench dashboard with more information that was needed to evaluate the release.

In the process of doing the contribution here, I realized how painful it is to contribute code to a json nested inside a configmap yaml.

I want to make this process easier first, and contribute the new dashboard panel after :)

Fix #420

[ArthurSens]

Anyone up for a review? 😬