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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,42 @@
+#ifndef DELEGATING_SECURITY_ENTITY_HPP_W1MFSVEN
+#define DELEGATING_SECURITY_ENTITY_HPP_W1MFSVEN
+
+#include <vanetza/security/security_entity.hpp>
+#include <vanetza/security/sign_service.hpp>
+#include <vanetza/security/verify_service.hpp>
+#include <memory>
+
+namespace vanetza
+{
+namespace security
+{
+
+/**
+ * Implementation of SecurityEntity delegating to SignService and VerifyService
+ */
+class DelegatingSecurityEntity : public SecurityEntity
+{
+public:
+    /**
+     * \brief Create security entity from primitive services.
+     *
+     * A std::invalid_argument exception is thrown at construction
+     * if any given service is not callable.
+     *
+     * \param sign SN-SIGN service
+     * \param verify SN-VERIFY service
+     */
+    DelegatingSecurityEntity(std::unique_ptr<SignService> sign, std::unique_ptr<VerifyService> verify);
+
+    EncapConfirm encapsulate_packet(EncapRequest&& encap_request) override;
+    DecapConfirm decapsulate_packet(DecapRequest&& decap_request) override;
+
+private:
+    std::unique_ptr<SignService> m_sign_service;
+    std::unique_ptr<VerifyService> m_verify_service;
+};
+
+} // namespace security
+} // namespace vanetza
+
+#endif /* DELEGATING_SECURITY_ENTITY_HPP_W1MFSVEN */