Improve config reload / change feedback

[fako1024]

When implementing #181 I noticed that gpctl (and hence the API / the CaptureManager) returns the interface changes even if they failed to execute (in this case because the interface in question was offline). This could be improved (e.g. by adding which failed, or not showing failed and printing the error(s) or coloring, or)...

▶ ./gpctl --server.addr=127.0.0.1:3005 config -r

     Enabled: [wlp0s20f3] <--
     Updated: []
    Disabled: []

DoD

• Extend API interface to return if an action succeeded / failed
• Colorize output to signify status on command line