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FLASHING.md says how to take a newer version of the colleague's tree (copy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/asn1/apply_patches.cmake

@@ -0,0 +1,10 @@
+find_package(Git REQUIRED)
+file(GLOB PATCH_FILES ${PATCH_DIRECTORY}/*.patch)
+foreach(PATCH_FILE IN LISTS PATCH_FILES)
+    get_filename_component(PATCH_NAME "${PATCH_FILE}" NAME_WE)
+    message(STATUS "Applying patch ${PATCH_NAME}")
+    execute_process(COMMAND "${GIT_EXECUTABLE}" apply "${PATCH_FILE}" RESULT_VARIABLE PATCH_RESULT)
+    if(NOT PATCH_RESULT EQUAL 0)
+        message(SEND_ERROR "Applying patch ${PATCH_FILE} failed!")
+    endif()
+endforeach()