TUN-8731: Implement diag/system endpoint

## Summary
This PR will add a new endpoint, "diag/system" to the metrics server that collects system information from different operating systems.

Closes TUN-8731

diagnostic/consts.go

@@ -0,0 +1,9 @@
+package diagnostic
+
+import "time"
+
+const (
+	defaultCollectorTimeout = time.Second * 10 // This const define the timeout value of a collector operation.
+	collectorField          = "collector"      // used for logging purposes
+	systemCollectorName     = "system"         // used for logging purposes
+)