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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,29 @@
+#include <vanetza/security/v3/static_certificate_provider.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v3
+{
+
+StaticCertificateProvider::StaticCertificateProvider(const Certificate& authorization_ticket,
+    const PrivateKey& authorization_ticket_key) :
+    authorization_ticket(authorization_ticket),
+    authorization_ticket_key(authorization_ticket_key)
+{
+}
+
+const PrivateKey& StaticCertificateProvider::own_private_key()
+{
+    return authorization_ticket_key;
+}
+
+const Certificate& StaticCertificateProvider::own_certificate()
+{
+    return authorization_ticket;
+}
+
+} // namespace v3
+} // namespace security
+} // namespace vanetza