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FLASHING.md says how to take a newer version of the colleague's tree (copy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/cmake/FindCryptoPP.cmake

@@ -0,0 +1,31 @@
+find_path(CryptoPP_INCLUDE_DIR NAMES cryptopp/config.h DOC "CryptoPP include directory")
+find_library(CryptoPP_LIBRARY NAMES cryptopp DOC "CryptoPP library")
+
+if(CryptoPP_INCLUDE_DIR)
+    # CRYPTOPP_VERSION has been moved to config_ver.h starting with Crypto++ 8.3
+    if(EXISTS ${CryptoPP_INCLUDE_DIR}/cryptopp/config_ver.h)
+        set(CryptoPP_VERSION_HEADER "config_ver.h")
+    else()
+        set(CryptoPP_VERSION_HEADER "config.h")
+    endif()
+    file(STRINGS ${CryptoPP_INCLUDE_DIR}/cryptopp/${CryptoPP_VERSION_HEADER} _config_version REGEX "CRYPTOPP_VERSION")
+    string(REGEX MATCH "([0-9])([0-9])([0-9])" _match_version "${_config_version}")
+    set(CryptoPP_VERSION_STRING "${CMAKE_MATCH_1}.${CMAKE_MATCH_2}.${CMAKE_MATCH_3}")
+endif()
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(CryptoPP
+    REQUIRED_VARS CryptoPP_INCLUDE_DIR CryptoPP_LIBRARY
+    FOUND_VAR CryptoPP_FOUND
+    VERSION_VAR CryptoPP_VERSION_STRING)
+
+if(CryptoPP_FOUND AND NOT TARGET CryptoPP::CryptoPP)
+    add_library(CryptoPP::CryptoPP UNKNOWN IMPORTED)
+    set_target_properties(CryptoPP::CryptoPP PROPERTIES
+        IMPORTED_LOCATION "${CryptoPP_LIBRARY}"
+        INTERFACE_INCLUDE_DIRECTORIES "${CryptoPP_INCLUDE_DIR}")
+endif()
+
+mark_as_advanced(CryptoPP_INCLUDE_DIR CryptoPP_LIBRARY)
+set(CryptoPP_INCLUDE_DIRS ${CryptoPP_INCLUDE_DIR})
+set(CryptoPP_LIBRARIES ${CryptoPP_LIBRARY})