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FLASHING.md says how to take a newer version of the colleague's tree (copy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/firmware/dependencies.lock

@@ -0,0 +1,21 @@
+dependencies:
+  espressif/esp-boost:
+    component_hash: 45cfa63ade2ad7c489203ab2ddf3f33be50ec9cab752b6eb17a79f06aee8f8f0
+    dependencies:
+    - name: idf
+      require: private
+      version: '>=5.3'
+    source:
+      registry_url: https://components.espressif.com/
+      type: service
+    version: 0.4.1
+  idf:
+    source:
+      type: idf
+    version: 6.0.2
+direct_dependencies:
+- espressif/esp-boost
+- idf
+manifest_hash: 3fca1283d556ade5b08c63857e23cb3b08582f1d1c24bb7c1d5e374f438415d7
+target: esp32c5
+version: 3.0.0