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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,23 @@
+#include <gtest/gtest.h>
+#include <vanetza/common/byte_sequence.hpp>
+#include <vanetza/security/v2/subject_info.hpp>
+#include <vanetza/security/v2/tests/check_subject_info.hpp>
+#include <vanetza/security/tests/serialization.hpp>
+
+using namespace vanetza::security::v2;
+
+TEST(SubjectInfo, Serialization)
+{
+    SubjectInfo sub;
+    sub.subject_type = SubjectType::Root_CA;
+    sub.subject_name = vanetza::random_byte_sequence(40);
+    check(sub, serialize_roundtrip(sub));
+}
+
+TEST(SubjectInfo, WebValidator_Size)
+{
+    SubjectInfo info;
+    info.subject_type = SubjectType::Authorization_Ticket;
+
+    EXPECT_EQ(2, get_size(info));
+}