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FLASHING.md says how to take a newer version of the colleague's tree (copy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/security/v2/encryption_parameter.hpp

@@ -0,0 +1,58 @@
+#ifndef ENCRYPTION_PARAMETER_HPP_EIAWNAWY
+#define ENCRYPTION_PARAMETER_HPP_EIAWNAWY
+
+#include <vanetza/security/v2/serialization.hpp>
+#include <boost/variant/variant.hpp>
+#include <array>
+#include <cstdint>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v2
+{
+
+/// forward declaration, see public_key.hpp
+enum class SymmetricAlgorithm : uint8_t;
+
+/// Nonce specified in TS 103 097 v1.2.1, section 4.2.7
+using Nonce = std::array<uint8_t, 12>;
+
+/// EncryptionParameter specified in TS 103 097 v1.2.1, section 4.2.7
+using EncryptionParameter = boost::variant<Nonce>;
+
+/**
+ * \brief Determines SymmetricAlgorithm for an EncryptionParameter
+ * \param param
+ * \return SymmetricAlgorithm
+ */
+SymmetricAlgorithm get_type(const EncryptionParameter&);
+
+/**
+ * \brief Serializes an EncryptionParameter into a binary archive
+ * \param ar to serialize in
+ * \param param to serialize
+ */
+void serialize(OutputArchive&, const EncryptionParameter&);
+
+/**
+ * \brief Calculates size of an EncryptionParameter
+ * \param param
+ * \return number of octets needed to serialize the EncryptionParameter
+ */
+size_t get_size(const EncryptionParameter&);
+
+/**
+ * \brief Deserializes an EncryptionParameter from a binary archive
+ * \param ar Input expected to start with an EncryptionParameter
+ * \param enc Deserialized encryption parameter
+ * \return size of deserialized EncryptionParameter
+ */
+size_t deserialize(InputArchive&, EncryptionParameter&);
+
+} // namespace v2
+} // namespace security
+} // namespace vanetzta
+
+#endif /* ENCRYPTION_PARAMETER_HPP_EIAWNAWY */