grafana template update that works with grafana v11.2.0

[sdutta9]

Proposed changes

Updates to the grafana template so that Prometheus datasource is templatized to make it work with latest version of grafana(v11.2.0 - grafana helm chart v8.5.1).

Related Discussions: #3032

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[github-actions]

✅ All required contributors have signed the F5 CLA for this PR. Thank you!
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[sdutta9]

I have hereby read the F5 CLA and agree to its terms

[jjngx]

@sdutta9 could you please add steps how you tested the new configuration?

[sdutta9]

@sdutta9 could you please add steps how you tested the new configuration?

Steps to setup

1. Install latest grafana via helm

    helm install nginx-grafana grafana/grafana --version 8.5.1 -n monitoring

2. Login to Grafana and add prometheus as your datasource.
3. In Dashboard pane, click on import dashboard.
4. Copy the contents of NGINXPlusICDashboard.json in the "Import via dashboard JSON model" box.
5. Click on "Load" button.
6. Once you click on "Load" button, it should show name, folder, UID fields pre populated.
7. Only thing that you need to select from drop down is your prometheus datasource for the prometheus section(See screenshot)
   
8. Click on "Import" after selecting your prometheus datasource, to finish the Dashboard import step.