feat: expose error metric when fetching message

[Abdulsametileri]

err := c.r.FetchMessage(c.context, m)
if err != nil {
     if c.context.Err() != nil {
        continue
      }

      c.metric.TotalErrorCountDuringFetchingMessage++
      c.logger.Warnf("Message could not read, err %s", err.Error())
      continue
}

Via this PR, clients use this metric for monitoring and alerting. Because some errors are not recoverable, it means, manual operation is required