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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,49 @@
+#include <vanetza/security/sha.hpp>
+#ifdef VANETZA_WITH_CRYPTOPP
+#include <cryptopp/sha.h>
+#endif
+#ifdef VANETZA_WITH_OPENSSL
+#include <openssl/sha.h>
+#endif
+
+namespace vanetza
+{
+namespace security
+{
+
+Sha256Digest calculate_sha256_digest(const uint8_t* data, std::size_t len)
+{
+    Sha256Digest digest;
+#if defined VANETZA_WITH_OPENSSL
+    static_assert(SHA256_DIGEST_LENGTH == digest.size(), "size of OpenSSL SHA256_DIGEST_LENGTH does not match");
+    SHA256_CTX ctx;
+    SHA256_Init(&ctx);
+    SHA256_Update(&ctx, data, len);
+    SHA256_Final(digest.data(), &ctx);
+#elif defined VANETZA_WITH_CRYPTOPP
+    static_assert(CryptoPP::SHA256::DIGESTSIZE == digest.size(), "size of CryptoPP::SHA256 does not match digest");
+    CryptoPP::SHA256 hash;
+    hash.CalculateDigest(digest.data(), data, len);
+#else
+#   error "no SHA256 implementation available"
+#endif
+    return digest;
+}
+
+Sha384Digest calculate_sha384_digest(const uint8_t* data, std::size_t len)
+{
+    Sha384Digest digest;
+#if defined VANETZA_WITH_OPENSSL
+    SHA384(data, len, digest.data());
+#elif defined VANETZA_WITH_CRYPTOPP
+    static_assert(CryptoPP::SHA384::DIGESTSIZE == digest.size(), "size of CryptoPP::SHA384 does not match digest");
+    CryptoPP::SHA384 hash;
+    hash.CalculateDigest(digest.data(), data, len);
+#else
+#   error "no SHA384 implementation available"
+#endif
+    return digest;
+}
+
+} // namespace security
+} // namespace vanetza