Better top help organisation

[pditommaso]

It could be desirable to group top commands separately, something like:

CORE COMMANDS:
  launch             Launch a pipeline execution 
  runs                 List and manages pipelines|workflow runs

MANAGE COMMANDS
  pipelines            Manage workspace pipelines launchpad
  actions              Manage actions
  compute-envs         Manage workspace compute environments
  credentials          Manage workspace credentials
  workspaces           Manage workspaces

ADDITIONAL COMMAND
  health               Checks system health status
  generate-completion  Generate bash/zsh completion script for towr.