Update kubectl exec syntax to remove deprecation warning (#2218)

Problem: Troubleshooting guide contains a deprecated kubectl command  syntax.

Solution: Fix the kubectl command.

Author: aknot242

site/content/how-to/monitoring/troubleshooting.md

@@ -73,7 +73,7 @@ LAST SEEN   TYPE      REASON              OBJECT
 Getting shell access to containers allows developers and operators to view the environment of a running container, see its logs or diagnose any problems. To get shell access to the NGINX container, use `kubectl exec`:
 
 ```shell
-kubectl exec -it -n nginx-gateway  <ngf-pod-name> -c nginx /bin/sh
+kubectl exec -it -n nginx-gateway  <ngf-pod-name> -c nginx -- /bin/sh
 ```
 
 #### Logs