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FLASHING.md says how to take a newer version of the colleague's tree (copy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-03/console.txt

@@ -0,0 +1,14 @@
+-- test_parameter_saps (free heap 113180, largest block 81920)
+-- test_trust_domain_and_pool (free heap 112192, largest block 81920)
+-- test_signing_profiles (free heap 111884, largest block 81920)
+-- test_fail_closed (free heap 111884, largest block 81920)
+-- test_fail_closed: unknown issuer (free heap 111884, largest block 81920)
+-- test_fail_closed: expired ticket (free heap 111884, largest block 81920)
+-- test_fail_closed: SN-DECAP (free heap 111884, largest block 81920)
+-- test_identifier_change (free heap 111884, largest block 81920)
+-- test_gn_core_identifier_change (free heap 111884, largest block 81920)
+-- test_sf_facilities_hook (free heap 111884, largest block 81920)
+-- test_ecies (free heap 111292, largest block 81920)
+-- test_enrolment_and_authorization (free heap 111292, largest block 81920)
+PASS: 503 checks (host/component tests, not ETSI ATS verdicts)
+VIDF_TEST_RESULT=0