add get cities handler and improve db schema

service_a/internal/domains/meteo/service.go

@@ -49,6 +49,10 @@ func (s *Service) UpdateElapsedMS(ctx context.Context, batchID, elapsedMS int) e
 	return nil
 }
 
+func (s *Service) GetCities(ctx context.Context) []string {
+	return s.repo.GetCities(ctx)
+}
+
 func (s *Service) GetMeteoData(ctx context.Context, params GetMeteoData) ([]MeteoData, error) {
 	return s.repo.GetMeteoData(ctx, params)
 }