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/handlers_test.go

@@ -35,7 +35,7 @@ func TestHandlerResolveAndFetch(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	h := NewHandler(parsed, up.Client())
+	h := NewHandler(parsed, up.Client(), nil)
 	req := httptest.NewRequest(http.MethodGet, "/api/agg/summary?aliases=test", nil)
 	rec := httptest.NewRecorder()
 	h.ServeHTTP(rec, req)
@@ -65,7 +65,7 @@ func TestHandlerMethodNotAllowed(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	h := NewHandler(parsed, http.DefaultClient)
+	h := NewHandler(parsed, http.DefaultClient, nil)
 	req := httptest.NewRequest(http.MethodPost, "/api/agg/summary", nil)
 	rec := httptest.NewRecorder()
 	h.ServeHTTP(rec, req)