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/certify/commands/generate-key.cpp

@@ -0,0 +1,56 @@
+#include "generate-key.hpp"
+#include <boost/program_options.hpp>
+#include <fstream>
+#include <iostream>
+#include <vanetza/security/backend.hpp>
+#include <vanetza/security/v2/persistence.hpp>
+
+namespace po = boost::program_options;
+using namespace vanetza::security;
+
+bool GenerateKeyCommand::parse(const std::vector<std::string>& opts)
+{
+    po::options_description desc("Available options");
+    desc.add_options()
+        ("help", "Print out available options.")
+        ("output", po::value<std::string>(&output)->required(), "Output file.")
+    ;
+
+    po::positional_options_description pos;
+    pos.add("output", 1);
+
+    po::variables_map vm;
+    po::store(po::command_line_parser(opts).options(desc).positional(pos).run(), vm);
+
+    if (vm.count("help")) {
+        std::cerr << desc << std::endl;
+
+        return false;
+    }
+
+    try {
+        po::notify(vm);
+    } catch (const std::exception& e) {
+        std::cerr << "Error: " << e.what() << std::endl << std::endl << desc << std::endl;
+
+        return false;
+    }
+
+    return true;
+}
+
+int GenerateKeyCommand::execute()
+{
+    auto backend = create_backend_or_throw("default");
+
+    std::cout << "Generating key... ";
+    auto key_pair = backend->generate_key_pair();
+    std::cout << "OK" << std::endl;
+
+    std::cout << "Writing key to '" << output << "'... ";
+    std::ofstream ofs(output, std::ios::binary);
+    v2::save_private_key_pkcs8_der(ofs, key_pair);
+    std::cout << "OK" << std::endl;
+
+    return 0;
+}