fix(prom-grafana docs): revamp prometheus and grafana pages (#809)

# Description

* fix instructions for Prometheus and Grafana installation
* revamp and restructure

## Related Issue

fix #758 

## Checklist

- [x] I have read the [contributing
documentation](https://retina.sh/docs/contributing).
- [x] I signed and signed-off the commits (`git commit -S -s ...`). See
[this
documentation](https://docs.github.com/en/authentication/managing-commit-signature-verification/about-commit-signature-verification)
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- [x] I have correctly attributed the author(s) of the code.
- [x] I have tested the changes locally.
- [x] I have followed the project's style guidelines.
- [x] I have updated the documentation, if necessary.
- [x] I have added tests, if applicable.

## Screenshots (if applicable) or Testing Completed

Please add any relevant screenshots or GIFs to showcase the changes
made.


![image](https://github.com/user-attachments/assets/9c5b742a-f4bd-4003-b2f4-078c2a5d319e)


![image](https://github.com/user-attachments/assets/5e1880f4-bd82-4a19-894c-82cf4482d900)


![image](https://github.com/user-attachments/assets/1d9c37df-480c-4409-9cf1-28e195fc7b3a)


## Additional Notes

Add any additional notes or context about the pull request here.

---

Please refer to the [CONTRIBUTING.md](../CONTRIBUTING.md) file for more
information on how to contribute to this project.

---------

Signed-off-by: Simone Rodigari <[email protected]>

docs/02-Installation/01-Setup.md

@@ -84,6 +84,7 @@ helm upgrade --install retina oci://ghcr.io/microsoft/retina/charts/retina \
     --set enableAnnotations=true
 ```
 
-## Next Steps: Configuring Prometheus/Grafana
+## Next Steps: Configuring Prometheus and Grafana
 
-- [Unmanaged Prometheus/Grafana](./04-Grafana/prometheus-unmanaged.md)
+- [Prometheus](./prometheus.md)
+- [Grafana](./grafana.md)

docs/02-Installation/04-prometheus.md

@@ -0,0 +1,47 @@
+# Prometheus
+
+Prometheus is an open-source system monitoring and alerting toolkit originally built at SoundCloud. It is now a standalone open source project and maintained independently of any company. Prometheus's main features include a multi-dimensional data model, a flexible query language, efficient time series database, and modern alerting approach. For more information, visit the [Prometheus website](https://prometheus.io).
+
+## Pre-Requisites
+
+1. Create a Kubernetes cluster.
+2. Install Retina DaemonSet (see [Quick Installation](./01-Setup.md)).
+
+## Install Prometheus via Helm
+
+1. In this example, we will install Prometheus via the community supported helm chart. If you already have this chart deployed, skip to step 3.
+
+  ```shell
+  helm repo add prometheus-community https://prometheus-community.github.io/helm-charts
+  helm repo update
+  ```
+
+1. Install the Prometheus chart
+
+  ```shell
+  helm install prometheus -n kube-system -f deploy/legacy/prometheus/values.yaml prometheus-community/kube-prometheus-stack
+  ```
+
+  Or if you already have the chart installed, upgrade how you see fit, providing the new job name as an additional scrape config, ex:
+
+  ```shell
+  helm upgrade prometheus -n kube-system -f deploy/legacy/prometheus/values.yaml prometheus-community/kube-prometheus-stack
+  ```
+
+> Note: Grafana and kube-state metrics may schedule on Windows nodes, the current chart doesn't have node affinity for those components. Some manual intervention may be required.
+
+## Access Prometheus UI
+
+1. Use port forwarding to accees Prometheus UI:
+
+  ```shell
+  kubectl port-forward --namespace kube-system svc/prometheus-operated 9090
+  ```
+
+1. Go to [localhost:9090/targets](http://localhost:9090/targets) to see the Retina Pods being discovered and scraped by Prometheus
+
+![Prometheus Retina Targets](./img/prometheus-retina-targets.png)
+
+## Next steps
+
+Follow [Configuring Grafana](./05-grafana.md) to visualise metrics in dashboards.

docs/02-Installation/05-grafana.md

@@ -0,0 +1,51 @@
+# Grafana
+
+Grafana is an open-source platform for monitoring and observability. It allows you to query, visualize, alert on, and explore your metrics no matter where they are stored. For more information, visit the [Grafana open-source section](https://grafana.com/oss/).
+
+## Pre-Requisites
+
+Make sure that you're still port-forwarding your server to [localhost:9090](http://localhost:9090) as part of [Prometheus](./04-prometheus.md) setup. Alternatively you can configure your server for some other HTTP endpoint, but that is not covered in the following instructions.
+
+## Configuring Grafana
+
+If you followed the steps to install and configure [Prometheus](./04-prometheus.md), you will already have Grafana installed as part of the `kube-prometheus-stack` Helm chart.
+
+1. Get Grafana user
+
+   ```shell
+   kubectl get secret -n kube-system prometheus-grafana -o jsonpath="{.data.admin-user}" | base64 --decode ; echo
+   ```
+
+2. Get Grafana password
+
+   ```shell
+   kubectl get secret -n kube-system prometheus-grafana -o jsonpath="{.data.admin-password}" | base64 --decode ; echo
+   ```
+
+3. Use port forwarding to access Grafana UI at [localhost:8080](http://localhost:8080) and enter you login credentials
+
+   ```shell
+   kubectl port-forward --namespace kube-system  svc/prometheus-grafana 8080:80
+   ```
+
+   ![Grafana login](./img/grafana-login.png)
+
+4. Make sure Prometheus is set as a default under Grafana datasources [localhost:8080/connections/datasources](http://localhost:8080/connections/datasources)
+
+   ![Grafana datasources](./img/grafana-datasources.png)
+
+5. Import the [kubernetes-networking-observability](https://grafana.com/grafana/dashboards/18814/) dashboard by id `18814` at [localhost:8080/dashboard/import](http://localhost:8080/dashboard/import)
+
+   ![Grafana import](./img/grafana-import.png)
+
+6. Kubernetes cluster metrics shouold be visible
+
+   ![Grafana kubernetes-networking-observability dashboard](./img/grafana-kubernetes-networking-dash.png)
+
+## Retina Dashboards
+
+There is a set of Retina dashboards that you can import directly into Grafana as json files. The dashboards are found under `deploy/legacy/grafana/dashboards/` if you installed retina legacy controlplane, and under `deploy/hubble/grafana/dashboards/` if you installed retina hubble controlplane.
+
+Here is an example of the Retina `dns.json` dashboard.
+
+![Grafana retina DNS dashboard](./img/grafana-retina-dns-dash.png)