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FLASHING.md says how to take a newer version of the colleague's tree (copy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/v3/trust_store.hpp

@@ -0,0 +1,37 @@
+#pragma once
+#include <vanetza/security/hashed_id.hpp>
+#include <vanetza/security/v3/certificate.hpp>
+#include <list>
+#include <map>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v3
+{
+
+class TrustStore
+{
+public:
+    /**
+     * Lookup certificates based on the passed HashedId8.
+     *
+     * \param id hash identifier of the certificate
+     * \return all stored certificates matching the passed identifier
+     */
+    std::list<Certificate> lookup(HashedId8 id) const;
+
+    /**
+     * Insert a certificate into store, i.e. consider it as trustworthy.
+     * \param trusted_certificate a trustworthy certificate copied into TrustStore
+     */
+    void insert(const Certificate& trusted_certificate);
+
+protected:
+    std::multimap<HashedId8, Certificate> m_certificates;
+};
+
+} // namespace v3
+} // namespace security
+} // namespace vanetza