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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,43 @@
+#ifndef SECURITY_ENTITY_HPP
+#define SECURITY_ENTITY_HPP
+
+#include <vanetza/security/decap_service.hpp>
+#include <vanetza/security/encap_service.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+
+class SecurityEntity
+{
+public:
+    /**
+     * \brief Creates a security envelope covering the given payload.
+     *
+     * The payload consists of the CommonHeader, ExtendedHeader and the payload of
+     * the layers above the network layer. The entire security envelope is used
+     * to calculate a signature which gets added to the resulting SecuredMessage.
+     *
+     * \param request containing payload to sign
+     * \return confirmation containing signed SecuredMessage
+     */
+    virtual EncapConfirm encapsulate_packet(EncapRequest&& request) = 0;
+
+    /**
+     * \brief Decapsulates the payload within a SecuredMessage
+     *
+     * Verifies the Signature and SignerInfo of a SecuredMessage.
+     *
+     * \param request containing a SecuredMessage
+     * \return decapsulation confirmation including plaintext payload
+     */
+    virtual DecapConfirm decapsulate_packet(DecapRequest&& request) = 0;
+
+    virtual ~SecurityEntity() = default;
+};
+
+} // namespace security
+} // namespace vanetza
+
+#endif // SECURITY_ENTITY_HPP