algo: Add STS Digi definition.

algo/data/sts/Digi.h

+/* Copyright (C) 2022 FIAS Frankfurt Institute for Advanced Studies, Frankfurt / Main
+   SPDX-License-Identifier: GPL-3.0-only
+   Authors: Felix Weiglhofer [committer]*/
+#ifndef CBM_ALGO_DATA_STS_DIGI_H
+#define CBM_ALGO_DATA_STS_DIGI_H
+
+#include "CbmStsDigi.h"
+
+namespace cbm::algo::sts
+{
+
+  using Digi = CbmStsDigi;
+
+}  // namespace cbm::algo::sts
+
+#endif  // CBM_ALGO_DATA_STS_DIGI_H