Add diagnostic_msgs as ROS2 dependency in CMakeLists.txt files

[paulerikf]

Had some trouble building v1.0.2 w/ ROS2 (foxy).

Build fails with:

In file included from 
</path/to/ws/src>/plotjuggler_ros/plugins/ros2_parsers/ros2_parser.cpp:7:0:
</path/to/ws/src>/plotjuggler_ros/plugins/ros2_parsers/diagnostic_msg.h:3:10: fatal error: diagnostic_msgs/msg/diagnostic_array.hpp: No such file or directory
 #include <diagnostic_msgs/msg/diagnostic_array.hpp>

Adding diagnostic_msgs to the ROS2 sections of the CMakeLists.txt files did the trick.

[facontidavide]

Thanks

[isakhammer]

Great stuff