Log User-Agent header

[redfast00]

At the moment, it's not clear what programs are calling endpoints (and how frequently). It would be nice to log the User-Agent header and log how frequently what User-Agent calls what endpoint.

Some concerns:

• just logging every request to a file would lead to more wear on the SD-card of the Pi (maybe logging to tmpfs could be possible)?
• having a global object and storing the stats in there might not work well, since there are multitple workers (but we can use https://docs.python.org/3/library/multiprocessing.html#managers)
• some scripts might not have a User-Agent header, or the header might be the same for two programs running on another machine, so it probably makes sense to also log the IP address

[FKD13]

I think it would not make much sense to try and do this ourselves. Since we already have a Grafana instance running, maybe we can use something like https://grafana.com/oss/loki/ . This way we don't have worry about aggregating stats ourselves and can we keep this application simpler.