add group field for a better command list formatting

[kindermax]

commands:
  lint:
    group: codequality
    cmd: eslint
  test:
    group: tests
    cmd: jest

and the output will be grouped and indented

Available commands:
  codequality
    lint
  tests
    test

[vharitonsky]

Doesn't it depend on spf13/cobra#836?

[kindermax]

I think it does not. We can implement it on our own, just by providing own template