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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,20 @@
+find_path(COHDA_ROOT
+    NAMES "ieee1609/app/lib1609/include/lib1609.h" "cohda/kernel/include/linux/cohda/llc/llc-api.h"
+    PATHS "/home/duser"
+    PATH_SUFFIXES mk5 mk2
+    CMAKE_FIND_ROOT_PATH_BOTH
+    DOC "Cohda SDK")
+
+set(COHDA_KERNEL_INCLUDE_DIR ${COHDA_ROOT}/ieee1609/kernel/include)
+set(COHDA_LIB1609_INCLUDE_DIR ${COHDA_ROOT}/ieee1609/app/lib1609/include)
+set(COHDA_LLC_INCLUDE_DIR ${COHDA_ROOT}/cohda/kernel/include/linux/cohda/llc)
+set(COHDA_INCLUDE_DIRS ${COHDA_KERNEL_INCLUDE_DIR} ${COHDA_LIB1609_INCLUDE_DIR} ${COHDA_LLC_INCLUDE_DIR})
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(Cohda "Cohda SDK not found" COHDA_ROOT)
+mark_as_advanced(COHDA_ROOT)
+if(COHDA_FOUND AND NOT TARGET Cohda::headers)
+    add_library(Cohda::headers UNKNOWN IMPORTED)
+    set_target_properties(Cohda::headers PROPERTIES
+        INTERFACE_INCLUDE_DIRECTORIES "${COHDA_INCLUDE_DIRS}")
+endif()