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FLASHING.md says how to take a newer version of the colleague's tree (copy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/dcc/transmit_rate_control.hpp

@@ -0,0 +1,52 @@
+#ifndef TRANSMIT_RATE_CONTROL_HPP_NOPDFSY6
+#define TRANSMIT_RATE_CONTROL_HPP_NOPDFSY6
+
+#include <vanetza/common/clock.hpp>
+#include <vanetza/dcc/transmission.hpp>
+
+namespace vanetza
+{
+namespace dcc
+{
+
+class TransmitRateThrottle
+{
+public:
+    /**
+     * Duration until next transmission has to be delayed
+     * \param tx transmission
+     * \return waiting time until next transmission is allowed
+     */
+    virtual Clock::duration delay(const Transmission& tx) = 0;
+
+    /**
+     * Current interval between packets
+     * \param tx transmission
+     * \return interval enforced by DCC_access
+     */
+    virtual Clock::duration interval(const Transmission& tx) = 0;
+
+    virtual ~TransmitRateThrottle() = default;
+};
+
+class TransmitRateFeedback
+{
+public:
+    /**
+     * Notify about an actual transmission at link layer
+     * \param tx transmission
+     */
+    virtual void notify(const Transmission& tx) = 0;
+
+    virtual ~TransmitRateFeedback() = default;
+};
+
+class TransmitRateControl : public TransmitRateThrottle, public TransmitRateFeedback
+{
+};
+
+} // namespace dcc
+} // namespace vanetza
+
+#endif /* TRANSMIT_RATE_CONTROL_HPP_NOPDFSY6 */
+