added prom2json check in api validation function

.functions/kubernetes.sh

@@ -58,5 +58,9 @@ function validate_private_ingress(){
 
 function k8s_list_deprecation_apis(){
     #Prints all api deprecation warnings in cluster
+    if ! command -v prom2json > /dev/null; then
+        printf "You need prom2json for this function: https://github.com/prometheus/prom2json\n"
+        return 1
+    fi
     kubectl get --raw /metrics | prom2json | jq -c '.[] | select(.name=="apiserver_requested_deprecated_apis").metrics[].labels' | column -t -s'{}[],"'
 }