fix(azure): query API management logs with not empty operations (#8598)

prowler/providers/azure/services/apim/apim_service.py

@@ -245,6 +245,7 @@ class APIM(AzureService):
         query = f"""
         ApiManagementGatewayLogs
         | where _ResourceId has '{instance.id}'
+        | where isnotempty(OperationId)
         | project TimeGenerated, OperationId, CallerIpAddress, CorrelationId
         """
         timespan = timedelta(minutes=minutes)