Is your feature related to a problem?

Yes, it's described here https://github.com/hoprnet/gitops/issues/253

Describe the feature you'd like

I would like to change the current hopr_up metric and name it hopr_start_time or similar, because the hopr_up is usually used to determine with the value of 0 or 1 if the process is running and what we are expressing is the start time. And add an additional metric named hopr_last_seeen or similar which would get the current timestamp of the node. This is necessary because we don't know the exact time at which the hoprd node failed and stopped sending metrics.