[idea] Make subcommands for subcommands

[kindermax]

Allow lets to have subcommands for subcommands, for example

lets user create
lets user delete

There are many ways to express it via yaml

Option A:

• pros:
  • explicit relation between commands, we see who is parent, who is child of some parent
  • we can grep parent: <> to see subcommands
• cons:
  • lots of changes in schema

commands:
  user:
    type: parent
    
  user_create:
    parent: user
    cmd: ...

  user_delete:
    parent: user
    cmd: ...

Option B:

• pros:
  • less changes that in A, only parent command
  • we can see in parent, which commands are subcommands and we can see it in one place
  • if some command is added to parent, it is hidden from commands output of lets help
• cons:
  • not explicit if command is a subcommand and if it is hidden

commands:
  user:
    commands:
      - user_create
      - user_delete
    
  user_create:
    cmd: ...

  user_delete:
     cmd: ...

Option C:

• pros:
  • less changes that in A, only add commands to Command
  • we can see in parent, which commands are subcommands and we can see it in one place
  • explicit that this is a subcommand and that it is not be shown in lets help
• cons:
  • one more layer of indentation

commands:
  user:
    commands:
       user_create:
         cmd: ...
      user_delete:
         cmd: ...