Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/external/vanetza-idf/tools/docker/update_cmake.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+source /etc/os-release
+export DEBIAN_FRONTEND=noninteractive
+
+install_kitware_repo() {
+    GPG_KEYFILE=/usr/share/keyrings/kitware-archive-keyring.gpg
+    wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/dev/null | gpg --dearmor > $GPG_KEYFILE
+    echo "deb [signed-by=$GPG_KEYFILE] https://apt.kitware.com/ubuntu/ ${UBUNTU_CODENAME} main" > /etc/apt/sources.list.d/kitware.list
+    echo "Added Kitware repository for Ubuntu $UBUNTU_CODENAME"
+}
+
+if [[ "${UBUNTU_CODENAME}" == "xenial" ]]; then
+    apt-get update && apt-get install -y apt-transport-https wget
+    install_kitware_repo
+elif [[ "${UBUNTU_CODENAME}" == "bionic" ]]; then
+    apt-get update && apt-get install -y gpg wget
+    install_kitware_repo
+else
+    # Ubuntu focal and later ship with a sufficiently new CMake version
+    echo "No need to add Kitware repository for Ubuntu $UBUNTU_CODENAME"
+fi