Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/external/vanetza-idf/vanetza/geonet/pdu_variant.hpp

@@ -0,0 +1,27 @@
+#ifndef PDU_VARIANT_HPP_AAEVKD5M
+#define PDU_VARIANT_HPP_AAEVKD5M
+
+#include <vanetza/geonet/extended_pdu.hpp>
+#include <vanetza/geonet/beacon_header.hpp>
+#include <vanetza/geonet/gbc_header.hpp>
+#include <vanetza/geonet/shb_header.hpp>
+#include <vanetza/geonet/tsb_header.hpp>
+#include <boost/variant.hpp>
+
+namespace vanetza
+{
+namespace geonet
+{
+
+typedef ExtendedPdu<ShbHeader> ShbPdu;
+typedef ExtendedPdu<TsbHeader> TsbPdu;
+typedef ExtendedPdu<BeaconHeader> BeaconPdu;
+typedef ExtendedPdu<GeoBroadcastHeader> GbcPdu;
+
+typedef boost::variant<BeaconPdu, GbcPdu, ShbPdu> PduVariant;
+
+} // namespace geonet
+} // namespace vanetza
+
+#endif /* PDU_VARIANT_HPP_AAEVKD5M */
+