feature request: show a @task's default argument values in help message

[davidxia]

Would be great if the help message showed a task's default argument values.

@task
def foo(ctx, a: int = 0, b: str = "b"):
    """My function"""
    print(f"a: {a}, b: {b}")

Right now it doesn't.

$ inv --help foo
Usage: inv[oke] [--core-opts] foo [--options] [other tasks here ...]

Docstring:
  My function

Options:
  -a INT
  -b STRING

I can use the @task's help parameter, but it would be nice to show each arg's default value without needing that.