Log something to indicate service is healthy and running

[peb-adr]

As of now the service seems to stay silent once startup is complete.
It would be nice to be able to see the service is still healthy and running by looking at the logs.
Maybe there is a recurring task that could be logged to fulfill this.

I was talking to @rrenkert considering logging for every new subscription, or alternatively only public-access subscriptions. This might be too much tho ..
@bastianjoel maybe you have an idea.

We could also consider regular metric logs like the autoupdate service is doing.

[bastianjoel]

I think logging metrics in a configurable interval like the autoupdate sounds good although I guess the only relevant metrics are:

• open connections
• projectors in pool