Mark SME2 matmul microkernel guide as draft

Set draft status for the SME2 matmul microkernel explanation.

Author: pareenaverma

content/learning-paths/mobile-graphics-and-gaming/kai_sme2_matmul_ukernel_explained/_index.md

@@ -1,6 +1,10 @@
 ---
 title: KleidiAI SME2 matmul microkernel for quantized models explained
 
+draft: true
+cascade:
+    draft: true
+    
 minutes_to_complete: 40
 
 who_is_this_for: This is an advanced topic for software developers, performance engineers, and AI practitioners 
@@ -57,4 +61,4 @@ further_reading:
 weight: 1                       # _index.md always has weight of 1 to order correctly
 layout: "learningpathall"       # All files under learning paths have this same wrapper
 learning_path_main_page: "yes"  # This should be surfaced when looking for related content. Only set for _index.md of learning path content.
----
+---