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/aggregate/geo_enrich.go

@@ -0,0 +1,41 @@
+package aggregate
+
+import (
+	"github.com/telemt/telemt-api/internal/geoip"
+)
+
+// EnrichUniqueIPsGeo fills country/city on each IP when lookup succeeds.
+func EnrichUniqueIPsGeo(rows []UniqueIPsRow, g *geoip.Service) {
+	if g == nil || len(rows) == 0 {
+		return
+	}
+	for i := range rows {
+		for j := range rows[i].IPs {
+			ip := rows[i].IPs[j].IP
+			res, ok := g.Lookup(ip)
+			if !ok {
+				continue
+			}
+			if res.CountryCode != "" {
+				s := res.CountryCode
+				rows[i].IPs[j].CountryCode = &s
+			}
+			if res.CountryName != "" {
+				s := res.CountryName
+				rows[i].IPs[j].CountryName = &s
+			}
+			if res.CityName != "" {
+				s := res.CityName
+				rows[i].IPs[j].CityName = &s
+			}
+			if res.ASN != 0 {
+				a := res.ASN
+				rows[i].IPs[j].ASN = &a
+			}
+			if res.ASOrg != "" {
+				o := res.ASOrg
+				rows[i].IPs[j].ASOrganization = &o
+			}
+		}
+	}
+}