This PR adds a new part to the integration test suite which spins up a
new headscale and runs through a scenario of test cases for each
command.
The intent is to check that all commands work as intended and produce
the expected output.
I think they have been pretty well covered, but would appreciate
additional test cases if I have missed some.
Please note: headscale is set up, and teared down for _each_ "test
function" in this file, this means that its more suitable for specific
cases.
