Make arm64 cpu image build optional

Signed-off-by: Kevin H. Luu <[email protected]>

Author: khluu

buildkite/test-template-ci.j2

@@ -546,10 +546,14 @@ steps:
         - exit_status: -10  # Agent was lost
           limit: 2
   {% endif %}
-  
+
+  - block: "Build Arm64 CPU image"
+    depends_on: ~
+    key: block-arm64-cpu-img-build
+    
   - label: ":docker: build image ARM64 CPU"
     key: image-build-arm64-cpu
-    depends_on: ~
+    depends_on: block-arm64-cpu-img-build
     agents:
       {% if branch == "main" %}
       queue: arm64_cpu_queue_postmerge