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FLASHING.md says how to take a newer version of the colleague's tree (copy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/tools/fuzz-harness/Dockerfile

@@ -0,0 +1,15 @@
+ARG VERSION=latest
+FROM aflplusplus/aflplusplus:${VERSION}
+
+# install build dependencies for Vanetza
+RUN apt-get update && apt-get install --no-install-recommends -y \
+    libboost-all-dev libcrypto++-dev libgeographic-dev libssl-dev
+
+# install casr-afl tool
+RUN cargo install --root /usr/local casr
+
+# set up "fuzz" user and mapping of host user
+RUN useradd -m -s /bin/bash fuzz
+RUN cp /root/.bashrc /home/fuzz/.bashrc && chown fuzz:fuzz /home/fuzz/.bashrc
+COPY docker-entrypoint.sh /docker-entrypoint.sh
+ENTRYPOINT ["/docker-entrypoint.sh"]