Add support for zsh (installed with minor modifications)

[olamarre]

I use zsh and was able to install this package with very little modifications to the source code. Steps to reproduce:

• System details (running in a docker container): ROS 2 Humble in Ubuntu 22.04 with the OS' default Python 3.10
• Install this package: sudo pip3 install ros-command
• Replace the following line in ros_command_setup.bash (directly edited the pip-installed file in the dist-packages directory):

argcomplete=$(which register-python-argcomplete{,3})

with

if which register-python-argcomplete >/dev/null 2>&1; then
    argcomplete=$(which register-python-argcomplete)
elif which register-python-argcomplete3 >/dev/null 2>&1; then
    argcomplete=$(which register-python-argcomplete3)
fi

• Source the modified file: source $(get_ros_command_bash)

With this modification alone, I can use roscd, roslaunch, rosmsg, etc.

Now, it seems that for full zsh support, a few more zsh-compatible scripts to mirror the bash-compatible ones would be needed (e.g., get_current_setup_zsh.py, get_ros_command_zsh.py, etc.)...