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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,20 @@
+#!/bin/bash
+set -e
+SCRIPT=$(readlink -f $0)
+SCRIPT_PATH=$(dirname $SCRIPT)
+ROOT=${1:-$SCRIPT_PATH/../..}
+ROOT_PATH=$(readlink -f ${ROOT})
+BUILD_DIR=${BUILD_DIR:-$PWD/build}
+
+mkdir -p ${BUILD_DIR} && cd ${BUILD_DIR}
+cmake -G Ninja \
+    -DVANETZA_WITH_CRYPTOPP=ON \
+    -DVANETZA_WITH_OPENSSL=ON \
+    -DBUILD_CERTIFY=ON \
+    -DBUILD_PKI=ON \
+    -DBUILD_SOCKTAP=ON \
+    -DBUILD_TESTS=ON \
+    -DGTest_BUILD_DIRECTORY_DOWNLOAD=ON \
+    ${ROOT_PATH}
+cmake --build .
+ctest --output-on-failure