[#170] Support tar.gz downloading

Split DownloadZip handler on methods. Add handler DownloadTar for downloading tar.gz archives. Make methods more universal for using in both implementations

Signed-off-by: Nikita Zinkevich <n.zinkevich@yadro.com>

internal/handler/utils.go

@@ -24,6 +24,13 @@ type request struct {
 	log *zap.Logger
 }
 
+func newRequest(ctx *fasthttp.RequestCtx, log *zap.Logger) request {
+	return request{
+		RequestCtx: ctx,
+		log:        log,
+	}
+}
+
 func (r *request) handleFrostFSErr(err error, start time.Time) {
 	logFields := []zap.Field{
 		zap.Stringer("elapsed", time.Since(start)),