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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,23 @@
+#pragma once
+#include <boost/geometry/core/cs.hpp>
+#include <boost/geometry/geometries/multi_polygon.hpp>
+#include <boost/geometry/geometries/point.hpp>
+#include <boost/geometry/geometries/polygon.hpp>
+
+namespace vanetza
+{
+namespace geodesy
+{
+namespace country
+{
+using CoordinateSystem = boost::geometry::cs::geographic<boost::geometry::degree>;
+using Point = boost::geometry::model::point<double, 2, CoordinateSystem>;
+using Ring = boost::geometry::model::ring<Point>;
+using Polygon = boost::geometry::model::polygon<Point>;
+using MultiPolygon = boost::geometry::model::multi_polygon<Polygon>;
+} // namespace country
+
+using CountryPolygon = country::MultiPolygon;
+
+} // namespace geodesy
+} // namespace vanetza