[hotfix] tag healthchecks for exclusion from prometheus message counter
context
- we count all messages written to the signald socket to a prometheus counter that we use to monitor traffic
- healtchecks (which go out in bursts of hundreds every 10 minutes) make the graphs for this counter very noisy
changes
- this introduces a conditional check in
socket.write
to differentiate healthchecks from other sent messages so we can exclude them from traffic graphs