chore: Update OPA version in template

Author: Techassi

docs/modules/opa/examples/getting_started/opa.yaml.j2

@@ -5,7 +5,7 @@ metadata:
   name: simple-opa
 spec:
   image:
-    productVersion: "1.8.0"
+    productVersion: "1.12.3"
   servers:
     roleGroups:
       default: {}