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FLASHING.md says how to take a newer version of the colleague's tree (copy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/tools/certify/utils.cpp

@@ -0,0 +1,35 @@
+#include "utils.hpp"
+#include <cstdint>
+#include <stdexcept>
+#include <sstream>
+
+void permission_string_to_buffer(const std::string& in, vanetza::ByteBuffer& out)
+{
+    if (in.size() / 8 != out.size() - 1 /* version */) {
+        std::stringstream ss;
+        ss << "Size mismatch, expected " << (out.size() - 1) << " bytes encoded with one bit per byte.";
+        throw std::runtime_error(ss.str());
+    }
+
+    uint8_t byte = 0;
+    int index = 0;
+
+    for (auto it = in.begin(); it < in.end(); ++it) {
+        byte <<= 1;
+
+        if (*it == '0') {
+            byte &= 0xFE; // clear last bit
+        } else if (*it == '1') {
+            byte |= 1; // set last bit
+        } else {
+            throw std::runtime_error("Unexpected character in permissions, expected only '0' and '1'.");
+        }
+
+        if ((index + 1) % 8 == 0) {
+            out.at(1 /* version */ + (index / 8)) = byte;
+            byte = 0;
+        }
+
+        ++index;
+    }
+}