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FLASHING.md says how to take a newer version of the colleague's tree (copy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/vanetza/asn1/patches/integer-oer-zero-length.patch

@@ -0,0 +1,13 @@
+diff --git a/vanetza/asn1/support/INTEGER_oer.c b/vanetza/asn1/support/INTEGER_oer.c
+index 8e0db3244..40dd53f4c 100644
+--- a/vanetza/asn1/support/INTEGER_oer.c
++++ b/vanetza/asn1/support/INTEGER_oer.c
+@@ -49,7 +49,7 @@ INTEGER_decode_oer(const asn_codec_ctx_t *opt_codec_ctx,
+         size -= consumed;
+     }
+ 
+-    if(req_bytes > size) {
++    if(req_bytes == 0 || req_bytes > size) {
+         ASN__DECODE_STARVED;
+     }
+