configuration: provide a way to disable GeoIP

[notABot101010]

The GeoIP feature is not free in term of performance, it loads the geoip database in memory (around 50MB, depending on your database) and adds a few microseconds (or nanoseconds for cached results) per request for the lookup.

While I think it's important to provide this feature enabled by default to make Pingoo easy to use, we may need to provide a way for advanced users to disable it.

Something like:

geoip:
  enabled: false

If someone has a better / more ergonomic idea, please let me know

[notABot101010]

Or maybe we take a bold decision and don't provide any way to disable geoip lookups. There is not situation where a few nanoseconds / microseconds per request is not acceptable.

The only thing to investigate is to reduce the memory footprint of the database, currently sitting at around 50MB. I think we can reduce it to ~20MB.