Add GeoIP support for unique IP aggregation

- Introduced GeoIP configuration options in config.example.yaml to enable geolocation lookups for the /api/agg/unique-ips endpoint.
- Updated the aggregate handler to include optional GeoIP data in responses, enriching unique IP information with country and city details, as well as ASN data if available.
- Enhanced documentation in AGGREGATE.md and README.md to reflect the new GeoIP functionality and its usage.
- Added a dependency on the geoip2-golang library in go.mod for GeoIP lookups.
- Modified tests to accommodate the new GeoIP integration in the aggregate handler.

internal/config/config.go

@@ -21,6 +21,17 @@ type Config struct {
 	TrustedProxies []string         `yaml:"trusted_proxies"`
 	Servers        []Server         `yaml:"servers"`
 	Aggregate      *AggregateConfig `yaml:"aggregate"`
+	GeoIP          *GeoIPConfig     `yaml:"geoip"`
+}
+
+// GeoIPConfig enables GeoLite2 lookups for /api/agg/unique-ips (optional).
+// Нужен хотя бы один из: database_path (City) или asn_database_path (ASN). Country-only DB не используется — страна в City.
+type GeoIPConfig struct {
+	Enabled          bool   `yaml:"enabled"`
+	DatabasePath     string `yaml:"database_path"`      // GeoLite2-City.mmdb
+	DownloadURL      string `yaml:"download_url"`       // если city-файла нет; .mmdb или .gz
+	AsnDatabasePath  string `yaml:"asn_database_path"`  // GeoLite2-ASN.mmdb
+	AsnDownloadURL   string `yaml:"asn_download_url"`   // если asn-файла нет
 }
 
 // AggregateConfig controls default scope of /api/agg/* (optional).