Docs: Fix broken link in loki.md (#21098)

Fixed broken video link

docs/sources/features/datasources/loki.md

@@ -69,7 +69,7 @@ Once the result is returned, the log panel shows a list of log rows and a bar ch
 
 <div class="medium-6 columns">
   <video width="800" height="500" controls>
-    <source src="/assets/videos/explore_loki.mp4" type="video/mp4">
+    <source src="https://grafana.com/static/assets/videos/explore_loki.mp4" type="video/mp4">
     Your browser does not support the video tag.
   </video>
 </div>