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/asn1/release2/TS103916v211/README.md

@@ -0,0 +1,8 @@
+The TS 103916 v2.1.1 POIM ASN1 files are copied from its [ETSI repository](https://forge.etsi.org/rep/ITS/asn1/poim_ts103916/-/tree/v2.1.1).
+The submodule TS 103916 v2.1.1 PA (Parking Availability) ASN1 files are copied instead from [ETSI repository](https://forge.etsi.org/rep/ITS/asn1/pa_ts103916/-/tree/release2?ref_type=heads), due to a missing bug fix.
+
+Finally, the current ASN1 definition is manually patched to:
+- Import GeoPosition field from CDD 2.2.1, instead of redefining it
+- Define locally the EngineCharacteristics (renamed EngineCharacteristicsFromIso) field to avoid generation of all fields from ISO17573-3-1.asn 
+
+See [ETSI License](https://forge.etsi.org/rep/ITS/asn1/poim_ts103916/-/blob/v2.1.1/LICENSE) for copyright details.