Refactor to query GeoIP in backend

[Gowee]

Querying GeoIP in browsers is a compromise due to the limitation of the previous Grafana plugins system (or its doc?). It complicates caching resolution results, slows down the load time, and exposes security risks when sharing panels.

Now it is possible to query GeoIP in a separated backend plugin.

The resources capability allows a backend plugin to handle custom HTTP requests sent to the Grafana HTTP API and respond with custom HTTP responses.

Ref:
https://grafana.com/docs/grafana/latest/developers/plugins/backend/#resources
https://github.com/grafana/grafana-plugin-sdk-go/blob/main/proto/backend.proto