Add Suite3 option with Ubuntu Focal

[sloretz]

Mimicking ros-infrastructure/catkin_pkg#271

[sloretz]

@wjwwood since it's been a while, I'm wondering if we should deprecate and not release vcstools, wstool, and rosinstall into Ubuntu Focal. Missing those dependencies hasn't blocked anything so far, and I don't see any use of python-vcstools, python-wstool, and python-rosinstall in the Melodic package.xml cache.

If so, this PR and #160 can be closed.

[wjwwood]

wstool is used in this documentation, I don't know if it will be the same for Noetic:

https://wiki.ros.org/melodic/Installation/Source#Create_a_catkin_Workspace

wstool depends on vcstools. I'm not sure about rosinstall, I know that it shares implementation details with wstool, but I don't know where it is used in the documentation at this time, but I would guess there are still plenty of places it is used.

[sloretz]

wstool is used in this documentation, I don't know if it will be the same for Noetic:

I replaced it with vcstool in the same section on the Noetic page: https://wiki.ros.org/noetic/Installation/Source#Create_a_catkin_Workspace

Anywhere else you're aware of it being used?

[wjwwood]

No, not without going through most of the wiki.ros.org docs, I couldn't say. I don't mind if we release this or not to be honest, but I expect there are still plenty of places that wstool is mentioned that will just stop working.

[dirk-thomas]

Closing since the repository is about to be archived: see #166.