Ability to group commands in the help

[joffrey-bion]

Just like we have OptionGroup to group options in the help, it would be nice to have a way to group subcommands.

In our Amper build tool, the help looks like this:

Usage: amper [<options>] <command> [<args>]...

Options:
  -v, --version                            Show the version and exit
  --root=<path>                            Amper project root
  --log-level=(debug|info|warn|error|off)  Console logging level (default: INFO)
  --shared-caches-root=<path>              Path to the cache directory shared between all Amper projects (default: C:\Users\Joffrey.Bion\AppData\Local\JetBrains\Amper)
  --async-profiler                         Profile Amper with Async Profiler
  --build-output=<path>                    Root directory for build outputs. By default, this is the build directory under the project root.
  -h, --help                               Show this message and exit

Commands:
  build                Compile and link all code in the project
  clean                Remove the project's build output and caches
  clean-shared-caches  Remove the Amper caches that are shared between projects
  generate-completion  Generate a tab-completion script for the Amper command for the given shell (bash, zsh, or fish)
  init                 Initialize a new Amper project based on a template
  package              Package the project artifacts for distribution
  publish              Publish modules to a repository
  run                  Run your application
  show                 Show information about some aspect the project (modules, tasks, effective settings...). See help for details.
  task                 Run a task and its dependencies from the task graph
  test                 Run tests in the project
  tool                 Run a tool
  update               Update Amper to the latest version

A subset of these commands are "global" commands (don't need a project), while others are project-level commands and need to be run in a project directory to work.
It would be nice to show them in 2 groups to make the distinction clearer.