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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,31 @@
+include(UseGTest)
+configure_gtest_directory(LINK_LIBRARIES geonet)
+
+add_gtest(Address address.cpp)
+add_gtest(Areas areas.cpp)
+add_gtest(BasicHeader basic_header.cpp)
+add_gtest(CbfPacketBuffer cbf_packet_buffer.cpp)
+add_gtest(CbrAggregator cbr_aggregator.cpp)
+add_gtest(CommonHeader common_header.cpp)
+add_gtest(DataConfirm data_confirm.cpp)
+add_gtest(DataRequest data_request.cpp)
+add_gtest(DccMcoField dcc_mco_field.cpp)
+add_gtest(DuplicatePacketList duplicate_packet_list.cpp)
+add_gtest(GbcGacHeader gbc_gac_header.cpp)
+add_gtest(GbcMemory
+    SOURCES gbc_memory.cpp network_topology.cpp)
+add_gtest(Lifetime lifetime.cpp)
+add_gtest(LocationTable location_table.cpp)
+add_gtest(PacketBuffer packet_buffer.cpp)
+add_gtest(PositionUpdater position_updater.cpp)
+add_gtest(PositionVector position_vector.cpp)
+add_gtest(Repeater repeater.cpp)
+add_gtest(Router router.cpp)
+add_gtest(RouterIndicate router_indicate.cpp
+    INCLUDE_DIRECTORIES ${PROJECT_SOURCE_DIR}/vanetza/security/tests)
+add_gtest(SequenceNumber sequence_number.cpp)
+add_gtest(Timestamp timestamp.cpp)
+add_gtest(TrafficClass traffic_class.cpp)
+add_gtest(Routing
+    SOURCES network_topology.cpp routing.cpp)
+add_gtest(RouterRequest router_request.cpp)