Add ElasticON hero (#1737)

Author: cotti

src/Elastic.Documentation.Site/_static/elasticon-2025-docs-page-banner-v3.png

@@ -34,7 +34,9 @@
 				}
 			</div>
 			<div class="flex justify-center items-center">
-				<img src="@Model.Static("web-documentation-hero-illustration.svg")" alt="" width="400">
+				<a href="https://www.elastic.co/events/elasticon" target="_blank">
+					<img src="@Model.Static("elasticon-2025-docs-page-banner-v3.png")" alt="Register now for ElasticON" width="1200">
+				</a>
 			</div>
 		</div>
 	</section>