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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,27 @@
+#ifndef BYTE_SEQUENCE_HPP_10RLFUNF
+#define BYTE_SEQUENCE_HPP_10RLFUNF
+
+#include <vanetza/common/byte_buffer.hpp>
+#include <functional>
+
+namespace vanetza
+{
+
+/**
+ * Create a random sequence of bytes
+ * \param length Length of generated byte buffer
+ * \param seed initializing random number generator
+ */
+ByteBuffer random_byte_sequence(std::size_t length, int seed = 0);
+
+/**
+ * Create generator function for random bytes
+ * \param seed initializing random number generator
+ * \return Generator function producing random bytes
+ */
+std::function<uint8_t()> random_byte_generator(int seed = 0);
+
+} // namespace vanetza
+
+#endif /* BYTE_SEQUENCE_HPP_10RLFUNF */
+