Allow bitnamilegacy image in chart values

Chart 11.4.2 refuses to render with an unrecognized image unless
global.security.allowInsecureImages is set (bitnami/charts#30850).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tasks/main.yml

@@ -9,6 +9,11 @@
     release_namespace: grafana
     create_namespace: true
     values:
+      global:
+        security:
+          # Required for bitnamilegacy images; the chart otherwise refuses to
+          # render (https://github.com/bitnami/charts/issues/30850).
+          allowInsecureImages: true
       image:
         repository: "{{ grafana_image_repository }}"
         tag: "{{ grafana_image_tag }}"