add a list command

[jaxxstorm]

I haven't used bubbletea for this because it feels like overkill. The command simply lists all of the active stacks.

Some thoughts:

• We should probably list the "type" of connection, although we'll need to plumb some stuff through so the stack to do this (automation API doesn't have tags?)
• We can use a bubbletea list for this if we think it's better, but not really intending to make this interactive for now