Add Ultralytics HUB Cloud Training banner to Docs (#8656)

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

docs/overrides/main.html

@@ -4,9 +4,9 @@
 
 {% block announce %}
    <div style="text-align: center;">
-       <a href="https://www.ultralytics.com/blog/ultralytics-yolov8-turns-one-a-year-of-breakthroughs-and-innovations"
+       <a href="https://hub.ultralytics.com/signup?utm_source=docs&utm_medium=banner&utm_campaign=cloud_training_release"
           target="_blank" style="color: #FFFFFF;">
-        Ultralytics YOLOv8 Turns One! 🎉 A Year of Breakthroughs and Innovations &nbsp; ➜
+          Introducing Ultralytics HUB Cloud Training! ☁️ Scalable. Simple. Smart. &nbsp; ➜
       </a>
    </div>
 {% endblock %}

docs/overrides/stylesheets/style.css

@@ -51,7 +51,7 @@ div.highlight {
 
 /* Update the background of the banner (same as the one on the Ultralytics website) */
 .md-banner {
-  background-image: url(https://assets-global.website-files.com/646dd1f1a3703e451ba81ecc/659fc4f4163e480e7ec280d0_banner.webp);
+  background-image: url(https://uploads-ssl.webflow.com/646dd1f1a3703e451ba81ecc/65e60cd6a4080bba757850a3_banner_ct.webp);
   background-size: cover;
   background-position: center;
 }