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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,65 @@
+#ifndef STATIC_CERTIFICATE_PROVIDER_HPP_MTULFLKX
+#define STATIC_CERTIFICATE_PROVIDER_HPP_MTULFLKX
+
+#include <vanetza/security/v2/certificate_provider.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v2
+{
+
+/**
+ * \brief A simple certificate provider
+ *
+ * This certificate provider uses a static certificate and key pair that is pre-generated.
+ */
+class StaticCertificateProvider : public CertificateProvider
+{
+public:
+    /**
+     * Create static certificate provider with empty chain
+     * \param authorization_ticket
+     * \param ticket_key private key of given authorization ticket
+     */
+    StaticCertificateProvider(const Certificate& authorization_ticket, const ecdsa256::PrivateKey& ticket_key);
+
+    /**
+     * Create static certificate provider with given chain
+     * \param authorization_ticket
+     * \param ticket_key private key of given authorization ticket
+     * \param chain own certificate chain
+     */
+    StaticCertificateProvider(const Certificate& authorization_ticket, const ecdsa256::PrivateKey& ticket_key,
+            const std::list<Certificate>& chain);
+
+    /**
+     * Get own certificate to use for signing
+     * \return own certificate
+     */
+    virtual const Certificate& own_certificate() override;
+
+    /**
+     * Get own certificate chain, excluding the leaf certificate and root CA
+     * \return own certificate chain
+     */
+    virtual std::list<Certificate> own_chain() override;
+
+    /**
+     * Get private key associated with own certificate
+     * \return private key
+     */
+    virtual const ecdsa256::PrivateKey& own_private_key() override;
+
+private:
+    Certificate authorization_ticket;
+    ecdsa256::PrivateKey authorization_ticket_key;
+    std::list<Certificate> chain;
+};
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza
+
+#endif /* STATIC_CERTIFICATE_PROVIDER_HPP_MTULFLKX */