Fix missing ROS2MedkitCompat.cmake in sensor_diagnostics Dockerfile

Preserve the shared CMake module from the ros2_medkit clone before
deleting it. Without this, colcon build fails because
ros2_medkit_serialization (and other packages) cannot resolve
their ../../cmake/ROS2MedkitCompat.cmake include path.

Fixes #28

Author: victorsolaz

demos/sensor_diagnostics/Dockerfile

@@ -32,6 +32,7 @@ RUN git clone --depth 1 https://github.com/selfpatch/ros2_medkit.git && \
     mv ros2_medkit/src/ros2_medkit_fault_manager . && \
     mv ros2_medkit/src/ros2_medkit_fault_reporter . && \
     mv ros2_medkit/src/ros2_medkit_diagnostic_bridge . && \
+    mkdir -p ${COLCON_WS}/cmake && mv ros2_medkit/cmake/ROS2MedkitCompat.cmake ${COLCON_WS}/cmake/ && \
     rm -rf ros2_medkit
 
 # Copy demo package