Include cluster_check: true on code snippets in sections that mention cluster checks (#29413)

This PR is to fix the missing `cluster_check: true` paramater in the code snippets on sections that mention cluster checks. This is required for cluster checks to work. This is just to keep it consistent with the actual cluster checks documentation here: https://docs.datadoghq.com/containers/cluster_agent/clusterchecks/?tab=datadogoperator

Author: mrdoggopat

content/en/containers/kubernetes/integrations.md

@@ -260,6 +260,7 @@ spec:
           <INTEGRATION_NAME>.yaml: |-
             ad_identifiers:
               - <CONTAINER_IMAGE>
+            cluster_check: true
             init_config:
               <INIT_CONFIG>
             instances:
@@ -303,6 +304,7 @@ clusterAgent:
     <INTEGRATION_NAME>.yaml: |-
       ad_identifiers:
         - <CONTAINER_IMAGE>
+      cluster_check: true
       init_config:
         <INIT_CONFIG>
       instances: