Changed how geoip cache is integrated with geoip processor.

[martijnvg]

This change helps facilitate allowing maxmind databases to be updated at runtime.
This will make is easier to purge the cache if a database changes.

Made the following changes:

• Changed how geoip processor integrates with the cache. The cache is moved from the geoip processor to DatabaseReaderLazyLoader class and by doing so caching is not directly a concern to the geoip processor implementation. In a followup change the DatabaseReaderLazyLoader instance a processor is using will change after a database update.
• Changed the cache key from ip + response class to ip + database_path.
• Moved GeoIpCache from IngestGeoIpPlugin class to be a top level class.

[elasticmachine]

Pinging @elastic/es-core-features (Team:Core/Features)

[probakowski]

LGTM, thanks @martijnvg !
I left one comment about possible simplification

[probakowski]

Maybe extract common functionality to separate method:

private <T extends AbstractResponse> T getResponse(InetAddress ipAddress, CheckedBiFunction<DatabaseReader, InetAddress, T,
    Exception> responseProvider) {
    SpecialPermission.check();
    return AccessController.doPrivileged((PrivilegedAction<T>) () ->
        cache.putIfAbsent(ipAddress, databasePath.toString(), ip -> {
            try {
                return responseProvider.apply(get(), ipAddress);
            } catch (AddressNotFoundException e) {
                throw new GeoIpProcessor.AddressNotFoundRuntimeException(e);
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }));
}

CityResponse getCity(InetAddress ipAddress) {
    return getResponse(ipAddress, DatabaseReader::city);
}

CountryResponse getCountry(InetAddress ipAddress) {
    return getResponse(ipAddress, DatabaseReader::country);
}

AsnResponse getAsn(InetAddress ipAddress) {
    return getResponse(ipAddress, DatabaseReader::asn);
}

[martijnvg]

Good idea!