Update course levels to reflect appropriate difficulty: change from beginner to intermediate/advanced

Signed-off-by: Lee Calcote <lee.calcote@layer5.io>

Author: leecalcote

content/learning-paths/d011fd20-a3f5-4480-883b-dfb34321d168/mastering-service-meshes-for-developers/introduction-to-service-meshes-istio/_index.md

@@ -6,7 +6,7 @@ weight: 1
 banner: "istio-icon-white.svg"
 tags: [service-mesh, istio]
 categories: "meshery"
-level: "intermediate"
+level: "advanced"
 ---
 
 A course to help you setup a service-mesh and start using it to build real-life applications using Meshery