Can't set sudo_args using CLI

[CreatureDev]

Bug description

When trying to launch a jupyterhub server using sudospawner, I am attempting to pass a -E argument to sudo in order to preserve the environment
When I do this it only returns that --SudoSpawner.sudo_args argument is of type 'str' when it needs to be a list
No matter how I edit this argument, it always evaluates to a string, making this option useless

Expected behaviour

the passed argument using --SudoSpawner.sudo_args argument for jupyterhub should result in the passed string being appended to the sudo args list, instead of parsed as a list itself

Actual behaviour

Passed value is used as a list, causing an error

How to reproduce

jupyterhub --JupyterHub.spawner_class=sudospawner.SudoSpawner --SudoSpawner.sudo_args=-E
jupyterhub --JupyterHub.spawner_class=sudospawner.SudoSpawner --SudoSpawner.sudo_args=[-E]
jupyterhub --JupyterHub.spawner_class=sudospawner.SudoSpawner --SudoSpawner.sudo_args="[-E]"

Your personal set up

• OS:

tested on
CentOS 7.9
Ubuntu 18.4

• Version(s):

python 3.6

• Full environment

# paste output of `pip freeze` or `conda list` here

• Configuration

# jupyterhub_config.py

• Logs

# paste relevant logs here, if any

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