add `source colcon-argcomplete.bash` somewhere

[SubaruArai]

I'd like to add tab completion for colcon. It should be possible to do so by adding this line to the end of .devcontainer/DockerFile:

RUN echo "source /usr/share/colcon_argcomplete/hook/colcon-argcomplete.bash" >> /home/ros/.bashrc

Is this a good approach? It's my first time trying to develop in a devcontainer, so please tell me it there's a better solution.

[athackst]

Great idea, I added it to the base docker images so that they'd all benefit from this idea