lib/geoip, cmd/relaypoolsrv, cmd/ursrv: Automatically manage GeoIP updates (#9342)

This adds a small package `geoip` which knows how to download and manage
the Maxmind GeoLite2 database we use. This removes the need for various
scripts to download and manage the geoip database, something that today
happens on Docker startup for the relay pool server and using various
hand written hacks for the usage reporting server.

The database is downloaded when needed and then refreshed on a
best-effort basis weekly.

Dockerfile.strelaypoolsrv

@@ -11,14 +11,6 @@ LABEL org.opencontainers.image.authors="The Syncthing Project" \
 
 EXPOSE 8080
 
-RUN apk add --no-cache ca-certificates su-exec curl
-ENV PUID=1000 PGID=1000 MAXMIND_KEY=
-
-RUN mkdir /var/strelaypoolsrv && chown 1000 /var/strelaypoolsrv
-USER 1000
-
 COPY strelaypoolsrv-linux-${TARGETARCH} /bin/strelaypoolsrv
-COPY script/strelaypoolsrv-entrypoint.sh /bin/entrypoint.sh
 
-WORKDIR /var/strelaypoolsrv
-ENTRYPOINT ["/bin/entrypoint.sh", "/bin/strelaypoolsrv", "-listen", ":8080"]
+ENTRYPOINT ["/bin/strelaypoolsrv", "-listen", ":8080"]