def for(metric_operation, metric_name = nil)
      list = if metric_name
               all.find { |manifest| manifest.metric_operation == metric_operation.to_s && manifest.metric_name == metric_name.to_s }
             else
               all.find_all { |manifest| manifest.metric_operation == metric_operation.to_s }
             end
      list
    end
def for(metric_operation, metric_name = nil)
      list = if metric_name
               all.find { |manifest| manifest.metric_operation == metric_operation.to_s && manifest.metric_name == metric_name.to_s }
             else
               all.find_all { |manifest| manifest.metric_operation == metric_operation.to_s }
             end
      list
    end
Searches for MetricOperationManifest(s) depending on parameters
 With 'metric_operation' only:
   - Returns all manifest related to that operation
 With 'metric_operation' and 'metric_name':
   - Returns a single manifest related to that two params