fix: add new dev NaaS URL

Author: cnbishop

src/Elastic.Documentation.Site/Layout/_AssemblerHeader.cshtml

@@ -3,8 +3,8 @@
 	<div id="elastic-nav" hx-disable="true"></div>
 	@{
 		var elasticNavUrl = Model.Features.StagingElasticNavEnabled
-			? "https://stag-www.elastic.co/elastic-nav.js"
-			: "https://www.elastic.co/elastic-nav.js";
+			? "https://www-elastic-co-pr-3017.app.elstc.co/elastic-nav.js"
+			: "https://www-elastic-co-pr-3017.app.elstc.co/elastic-nav.js";
 	}
 	<script src="@elasticNavUrl" async></script>
 </div>