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FLASHING.md says how to take a newer version of the colleague's tree (copy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/socktap/certificate_validation_v3.hpp

@@ -0,0 +1,64 @@
+#pragma once
+
+#include <vanetza/security/private_key.hpp>
+#include <memory>
+#include <string>
+
+namespace boost
+{
+namespace program_options
+{
+class options_description;
+class variables_map;
+} // namespace program_options
+} // namespace boost
+
+namespace vanetza
+{
+
+class PositionProvider;
+class Runtime;
+
+namespace security
+{
+
+class Backend;
+
+namespace v3
+{
+class Certificate;
+class CertificateValidator;
+class LocationChecker;
+} // namespace v3
+} // namespace security
+} // namespace vanetza
+
+/**
+ * Owns the profile-specific services selected for a socktap V3 security context.
+ *
+ * Profile-specific implementations may retain issuer certificates and trust
+ * anchors needed by their validator and select the credential format expected
+ * by that profile. The strict implementation preserves socktap's established
+ * behavior.
+ */
+class CertificateValidationV3
+{
+public:
+    virtual ~CertificateValidationV3() = default;
+
+    virtual vanetza::security::v3::CertificateValidator& validator() = 0;
+    virtual vanetza::security::PrivateKey load_authorization_ticket_key(
+        const std::string&) const = 0;
+    virtual void add_chain_certificate(const vanetza::security::v3::Certificate&) = 0;
+};
+
+std::unique_ptr<CertificateValidationV3> create_default_certificate_validation_v3(
+    const vanetza::Runtime&, vanetza::PositionProvider&,
+    const vanetza::security::v3::LocationChecker&);
+
+std::unique_ptr<CertificateValidationV3> create_certificate_validation_v3(
+    const boost::program_options::variables_map&, const vanetza::Runtime&,
+    vanetza::PositionProvider&, const vanetza::security::v3::LocationChecker&,
+    vanetza::security::Backend&);
+
+void add_certificate_validation_v3_options(boost::program_options::options_description&);