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FLASHING.md says how to take a newer version of the colleague's tree (copy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/support/UTCTime_rfill.c

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2017 Lev Walkin <vlm@lionet.info>.
+ * All rights reserved.
+ * Redistribution and modifications are permitted subject to BSD license.
+ */
+#include "asn_internal.h"
+#include "UTCTime.h"
+
+asn_random_fill_result_t
+UTCTime_random_fill(const asn_TYPE_descriptor_t *td, void **sptr,
+                    const asn_encoding_constraints_t *constraints,
+                    size_t max_length) {
+    asn_random_fill_result_t result_ok = {ARFILL_OK, 1};
+    asn_random_fill_result_t result_failed = {ARFILL_FAILED, 0};
+    asn_random_fill_result_t result_skipped = {ARFILL_SKIPPED, 0};
+    static const char *values[] = {
+        "700101000000",  "700101000000-0000", "700101000000+0000",
+        "700101000000Z", "821106210623",      "691106210827-0500",
+        "821106210629Z",
+    };
+    size_t rnd = asn_random_between(0, sizeof(values)/sizeof(values[0])-1);
+
+    (void)constraints;
+
+    if(max_length < sizeof("yymmddhhmmss") && !*sptr) {
+        return result_skipped;
+    }
+
+    if(*sptr) {
+        if(OCTET_STRING_fromBuf(*sptr, values[rnd], -1) != 0) {
+            if(!sptr) return result_failed;
+        }
+    } else {
+        *sptr = OCTET_STRING_new_fromBuf(td, values[rnd], -1);
+        if(!sptr) return result_failed;
+    }
+
+    return result_ok;
+}