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/pki/distribution_centre.cpp

@@ -0,0 +1,60 @@
+#include "distribution_centre.hpp"
+#include "http.hpp"
+
+namespace vanetza
+{
+namespace pki
+{
+
+DistributionCentre::DistributionCentre()
+{
+}
+
+void DistributionCentre::set_url(const std::string& url)
+{
+    m_base_query = HttpQuery::from_url(url);
+}
+
+boost::optional<CertificateTrustList> DistributionCentre::fetch_trust_list(const HashedId8& digest)
+{
+    HttpQuery query = m_base_query;
+    query.path += "/getctl/" + hexstring(digest);
+
+    HttpResponse response = http_get(query);
+    if (response.result() != boost::beast::http::status::ok) {
+        return boost::none;
+    } else if (response[boost::beast::http::field::content_type] != "application/x-its-ctl") {
+        return boost::none;
+    }
+
+    CertificateTrustList trust_list;
+    if (trust_list.decode(response.body())) {
+        return trust_list;
+    } else {
+        return boost::none;
+    }
+}
+
+boost::optional<CertificateRevocationList> DistributionCentre::fetch_revocation_list(const HashedId8& digest)
+{
+    // TS 102 941 v1.4.1 Annex D.2: GET <dc>/getcrl/<UPPERCASE-HEX-HashedId8>; reply application/x-its-crl.
+    HttpQuery query = m_base_query;
+    query.path += "/getcrl/" + hexstring(digest);
+
+    HttpResponse response = http_get(query);
+    if (response.result() != boost::beast::http::status::ok) {
+        return boost::none;
+    } else if (response[boost::beast::http::field::content_type] != "application/x-its-crl") {
+        return boost::none;
+    }
+
+    CertificateRevocationList crl;
+    if (crl.decode(response.body())) {
+        return crl;
+    } else {
+        return boost::none;
+    }
+}
+
+} // namespace pki
+} // namespace vanetza