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FLASHING.md says how to take a newer version of the colleague's tree (copy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/docs/idf/evidence/security-device-08/result.json

@@ -0,0 +1,13 @@
+{
+  "kind": "component-tests",
+  "target": "esp32c5",
+  "idf_version": "6.0.2",
+  "port": "COM11",
+  "status": "pass",
+  "reset": "none",
+  "checks": 765,
+  "backend": "BackendMbedTls (PSA Crypto, mbedTLS 4.1.0 of ESP-IDF 6.0.2) with CONFIG_MBEDTLS_HARDWARE_ECDSA_VERIFY; 765 checks = 890 host checks minus the OpenSSL-only oracle tests",
+  "capture": "listen-only after the esptool post-flash reset",
+  "verifies": "as security-device-07 plus test_credentials: credential bundle round trip, malformed bundles refused, apply() through the entity's checks, NvsCredentialStore save/load/erase on the nvs_flash partition (CONFIG_VANETZA_IDF_NVS_CREDENTIALS=y, NVS initialised by the test application)",
+  "sha256": "ab9384f0150c90de84c5187a68363de4c13dc53781660cb4e8a473bdee69c3df"
+}