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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,29 @@
+#include <gtest/gtest.h>
+#include <vanetza/security/v2/tests/check_certificate.hpp>
+#include <vanetza/security/v2/tests/check_list.hpp>
+#include <vanetza/security/v2/tests/check_signature.hpp>
+#include <vanetza/security/v2/tests/check_signer_info.hpp>
+#include <vanetza/security/v2/tests/check_subject_attribute.hpp>
+#include <vanetza/security/v2/tests/check_subject_info.hpp>
+#include <vanetza/security/v2/tests/check_validity_restriction.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v2
+{
+
+void check(const Certificate& expected, const Certificate& actual)
+{
+    // certificate version is static, no check required
+    check(expected.signer_info, actual.signer_info);
+    check(expected.subject_info, actual.subject_info);
+    check(expected.subject_attributes, actual.subject_attributes, "SubjectAttribute");
+    check(expected.validity_restriction, actual.validity_restriction, "ValidityRestriction");
+    check(expected.signature, actual.signature);
+}
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza