Create artifacts for metrics only for CNG related test

This change adds a conditional check to the metrics collection process. Previously, the system would always attempt to collect performance metrics from a server instance. Now, it only collects these metrics when a specific configuration flag called "RUN_ON_CNG" is set to true. This allows the system to skip the metrics collection step in certain scenarios, making the process more flexible based on the deployment environment or configuration settings.

Related to : #116