Add x-elastic-product-origin to header (#203447)

Related to: https://github.com/elastic/observability-dev/issues/4147

Adds the `x-elastic-product-origin` when invoking the kibana function

x-pack/plugins/observability_solution/observability_ai_assistant/server/functions/kibana.ts

@@ -77,6 +77,7 @@ export function registerKibanaFunction({
         'referer',
         'user-agent',
         'x-elastic-internal-origin',
+        'x-elastic-product-origin',
         'x-kbn-context',
       ];