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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,54 @@
+#ifndef FD3D1A69_8B8D_4DC1_8975_9FEB7A791B56
+#define FD3D1A69_8B8D_4DC1_8975_9FEB7A791B56
+
+#include <vanetza/security/secured_message.hpp>
+#include <vanetza/security/sign_service.hpp>
+#include <boost/variant/variant.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+
+/**
+ * Input data for encapsulating a packet in a secured message.
+ * 
+ * According to TS 102 723-8 V1.1.1, SN-ENCAP.request offers the very same
+ * functionality as SN-SIGN.request and SN-ENCRYPT.request.
+ * 
+ * Since encryption is not yet implemented, so only SignRequest is included.
+ */
+using EncapRequest = boost::variant<SignRequest>;
+
+/**
+ * Confirmation of the encapsulation process (SN-ENCAP.confirm).
+ * 
+ * TS 102 723-8 V1.1.1 includes only sec_packet but cannot report any errors.
+ * Instead of throwing exceptions, the variant may convey an error code instead
+ * of a SecuredMessage.
+ */
+struct EncapConfirm : public boost::variant<SecuredMessage, SignConfirmError>
+{
+public:
+    static EncapConfirm from(SignConfirm&&);
+
+    const SecuredMessage* secured_message() const;
+    SecuredMessage* secured_message();
+
+private:
+    using variant::variant;
+};
+
+/**
+ * Dispatch an encapsulation request to the responsible service.
+ * 
+ * \param encap_request SN-ENCAP.request data
+ * \param sign_service service handling signing requests
+ * \return SN-ENCAP.confirm
+ */
+EncapConfirm dispatch(EncapRequest&& encap_request, SignService* sign_service);
+
+} // namespace security
+} // namespace vanetza
+
+#endif /* FD3D1A69_8B8D_4DC1_8975_9FEB7A791B56 */