[feature request] Exclude function (kw)args from synopsis, arguments and flags in help output

[eelkevdbos]

The help output lists all function (keyword) arguments in the synopsis, arguments and flags.

In my specific use case, I would like to exclude some of those arguments, because they are:

1. of non-literal type, and therefore not easily provided through the means of CLI
2. injected by a dependency injection decorator

The option to exclude (keyword) arguments could be done in a couple of ways:

1. prefix the argument name with an underscore, e.g.

def my_function(a: bool, _complex_type: ComplexType = ComplexType()):
  ...

2. limit args and kwargs to literal types

fire.Fire(help_include_literals_only=True)

3. provide the means to exclude arguments based on module or instance type, e.g.

def my_function(a: bool, s: service.ComplexType):
  ...

fire.Fire(
  help_exclude_arg_types=[service.ComplexType],
  help_exclude_arg_modules=[service]
)