Document output order of catkin list

[rgov]

System Info

• Operating System: Linux lrauv-vm 4.15.0-135-generic #139-Ubuntu SMP Mon Jan 18 17:38:24 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
• Python Version: 2.7.17
• Version of catkin_tools: 0.6.1
• ROS Distro: Melodic

Expected Behavior

catkin list does not define a sort order of the packages returned. It may be based on a topological sort based on build dependencies, but I'm not completely sure about that.

It would be nice to at least document the existing behavior so that one can tell whether further sorting of the package list is necessary for their purposes.

Since catkin already has the ability to topologically sort the dependency list, it would be nice if you could ask for --sort=build or --sort=run or something like that to choose which dependency list you care about. Then users wouldn't need to write any code to parse the yaml output and sort it themselves.