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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,61 @@
+ARG DEBIAN_VERSION=stable
+ARG UBUNTU_VERSION=resolute
+
+FROM debian:${DEBIAN_VERSION} AS debian
+ARG DEBIAN_FRONTEND=noninteractive
+SHELL ["/bin/bash", "-c"]
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        build-essential \
+        ca-certificates \
+        capnproto \
+        clang \
+        cmake \
+        git \
+        libboost-date-time-dev \
+        libboost-program-options-dev \
+        libboost-system-dev \
+        libcapnp-dev \
+        libcrypto++-dev \
+        libgeographiclib-dev \
+        libssl-dev \
+        ninja-build \
+        pkg-config \
+    && rm -rf /var/lib/apt/lists/*
+COPY --chmod=755 build_and_run_tests.sh build_strict_cxx14.sh /usr/local/bin/
+RUN useradd -m build-user
+USER build-user
+WORKDIR /home/build-user
+ENTRYPOINT ["build_and_run_tests.sh"]
+CMD ["/home/build-user/workspace"]
+
+FROM debian AS strict-cxx14
+ENTRYPOINT ["build_strict_cxx14.sh"]
+CMD ["/home/build-user/workspace"]
+
+FROM ubuntu:${UBUNTU_VERSION} AS ubuntu
+ARG DEBIAN_FRONTEND=noninteractive
+SHELL ["/bin/bash", "-c"]
+COPY --chmod=755 update_cmake.sh apt_pkg_name.sh /usr/local/bin/
+RUN update_cmake.sh && apt-get update && \
+    apt-get install -y --no-install-recommends \
+        build-essential \
+        ca-certificates \
+        capnproto \
+        cmake \
+        git \
+        libboost-date-time-dev \
+        libboost-program-options-dev \
+        libboost-system-dev \
+        libcapnp-dev \
+        libcrypto++-dev \
+        $(apt_pkg_name.sh geographiclib) \
+        libssl-dev \
+        ninja-build \
+        pkg-config \
+    && rm -rf /var/lib/apt/lists/*
+COPY build_and_run_tests.sh /usr/local/bin/build_and_run_tests.sh
+RUN useradd -m build-user
+USER build-user
+WORKDIR /home/build-user
+ENTRYPOINT ["build_and_run_tests.sh"]
+CMD ["/home/build-user/workspace"]