fix: configure Grafana for iframe embedding in dashboard

Added required Grafana environment variables for proper iframe embedding:
- GF_SERVER_SERVE_FROM_SUB_PATH=true: Allows serving from /embedded/grafana
- GF_SERVER_ROOT_URL: Configures correct URL context with dynamic domain
- GF_SECURITY_ALLOW_EMBEDDING=true: Permits iframe embedding
- GF_AUTH_ANONYMOUS_ENABLED=false: Keeps authentication required

This fixes the "localhost refused to connect" error after login by ensuring
Grafana uses the correct URL context instead of redirecting to localhost.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: szedan-rh

deploy/openshift/observability/grafana/deployment.yaml

@@ -48,6 +48,14 @@ spec:
           value: ""
         - name: GF_PATHS_PROVISIONING
           value: /etc/grafana/provisioning
+        - name: GF_SERVER_SERVE_FROM_SUB_PATH
+          value: "true"
+        - name: GF_SERVER_ROOT_URL
+          value: "%(protocol)s://%(domain)s/embedded/grafana"
+        - name: GF_SECURITY_ALLOW_EMBEDDING
+          value: "true"
+        - name: GF_AUTH_ANONYMOUS_ENABLED
+          value: "false"
         volumeMounts:
         - name: storage
           mountPath: /var/lib/grafana