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.

config.example.yaml

@@ -29,6 +29,14 @@ trusted_proxies: []
 #     - gt1
 #     - gt2
 
+# Геолокация IP в /api/agg/unique-ips. См. docs/GEOIP.md (City + опционально ASN; Country-only не нужен)
+# geoip:
+#   enabled: true
+#   database_path: /var/lib/telemt-gateway/GeoLite2-City.mmdb
+#   download_url: "https://github.com/P3TERX/GeoLite.mmdb/raw/download/GeoLite2-City.mmdb"
+#   asn_database_path: /var/lib/telemt-gateway/GeoLite2-ASN.mmdb
+#   asn_download_url: "https://github.com/P3TERX/GeoLite.mmdb/raw/download/GeoLite2-ASN.mmdb"
+
 servers:
   - alias: main_srv
     base_url: http://127.0.0.1:9091