add more human readable formatting for `clusterctl <> get` commands

[mapuri]

The clusterctl <> get commands only print the JSON response on the screen, which is more machine readable can be desirable in a few cases (for example to render the data on a Web UI), but a more human readable output is desirable for command line.

This issue tracks general design for formatting the output of the commands in a more human readable format. Preferably it will apply to all get commands.

/cc @vvb. This is based on our recent discussions. Feel free to share ideas, proposals etc here. I will also look around for what other projects have done.