CORS Error: "Origin Not Allowed" When Adding Data Source Behind NGINX Reverse Proxy Grafana v11.4.1 (bcb04ab63b)

### What happened? I deployed Grafana using Helm on Kubernetes and placed it behind an NGINX reverse proxy. However, when trying to add a data source or import a dashboard, I get the following error: "Orgin not Allowed" ### What did you expect to happen? Grafana should allow requests from the NGINX reverse proxy without CORS errors. I should be able to add a data source and import dashboards successfully. No "Origin Not Allowed" error should occur in the browser console. ### Did this work before? No, this issue has been present since the initial deployment. ### How do we reproduce it? Deploy Grafana using the Prometheus Helm stack on Kubernetes. Helm Chart: kube-prometheus-stack Grafana Version: 10.0.3 Configure NGINX as a reverse proxy with CORS settings. Access Grafana via the NGINX domain (e.g., https://grafana.example.com). Try to add a data source or import a dashboard. Observe the error: "Origin Not Allowed" appears in the browser console. ### Is the bug inside a dashboard panel? No, the issue occurs when trying to add a data source or import a dashboard. ### Environment (with versions)? Grafana: v11.4.1 OS: CentOS 9 Browser: chrome/firefox ### Grafana platform? Kubernetes ### Datasource(s)? prometheus