Improve error handling v2

[MartinKolarik]

Partly related to #106.

Currently, when I use a command incorrectly, there's an error followed by the (long) help text, so I can't actually see the error and need to scroll up for it:

=>

This gets quite annoying as the error message is usually more useful for fixing the problem than the help text. In comparison, curl only prints the error and a hint to run curl --help for the help:

How about we do it similarly and print Run 'globalping --help' for more information. In case the error happened with a specific sub-command, the message would include that command, e.g. Run 'globalping ping --help' for more information.

[MartinKolarik]

@radulucut please:

• keep everything as is for cases where we already use silenceUsage (don't add even the single line),
• do what I described above for cases where we currently show the full help.