docs: add section on importing the Grafana dashboard using the Grafana Helm Chart

[maritiren]

Description

Adding section on how to import the dashboard using the Grafana Helm Chart. I think this is helpful as many use the Grafana Helm chart to set it up.

From the Grafana spec:
https://github.com/grafana/helm-charts/blob/grafana-8.0.2/charts/grafana/values.yaml#L708-L759

Checklist

• I've read the guidelines for contributing to this repository.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[chen-keinan]

@maritiren lgtm 🚀