cmd/hide/main: use cobra to run hide

[aleh-null]

TODO:

• wire in cobra
• organize code as in guide
• run/server sub commands to current main as hide run/server ...

--help and --version flags are enabled, version only prints some mock information

[artmoskvin]

With the current project layout, the paths become a bit weird, e.g. hide/cmd/hide/pkg/cmd. I think we can simplify it by separating hide/cmd and hide/pkg. In the hide/cmd package we'll have everything related to commands and in hide/pkg all the internal stuff as we have now. By the way, we can rename it into internal because I don't think we plan for it to be used externally.