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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,37 @@
+#ifndef STATE_MACHINE_HPP_0MHYOQU7
+#define STATE_MACHINE_HPP_0MHYOQU7
+
+#include <vanetza/dcc/channel_load.hpp>
+#include <vanetza/common/clock.hpp>
+
+namespace vanetza
+{
+namespace dcc
+{
+
+/**
+ * State machine interface used for Transmit Rate Control
+ */
+class StateMachine
+{
+public:
+    /**
+     * Trigger state transition by updated channel load
+     * \param cl new channel load measurement
+     */
+    virtual void update(ChannelLoad cl) = 0;
+
+    /**
+     * Get current transmission interval
+     * \return duration between two transmissions
+     */
+    virtual Clock::duration transmission_interval() const = 0;
+
+    virtual ~StateMachine() = default;
+};
+
+} // namespace dcc
+} // namespace vanetza
+
+#endif /* STATE_MACHINE_HPP_0MHYOQU7 */
+