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FLASHING.md says how to take a newer version of the colleague's tree (copy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/radio-pair-01/result.json

@@ -0,0 +1,18 @@
+{
+  "kind": "radio-integration",
+  "dut": "COM20",
+  "receiver": "COM11",
+  "channel": 180,
+  "status": "pass",
+  "captures": [
+    {
+      "rssi_dbm": -46,
+      "device_timestamp_us": 48779796,
+      "trailing_bytes": "00009900",
+      "exact_match": true
+    }
+  ],
+  "cleanup_errors": [],
+  "receive_only_tx_rejected": true,
+  "submission_accepted": true
+}