Description of the problem, including code/CLI snippet

Hello,
First of all thank you for the work done in this project, it is helpful.

I am trying to manage some gitlab configuration with python-gitlab CLI, however I do not find the right syntax to protect a branch. I am struggling with the parameters :

--allowed-to-push
--allowed-to-merge

Can someone help me ?

**The syntax below does not work

   gitlab project-protected-branch create --project-id xxx\
      --name master \
      --allowed-to-merge='user_id: xxx' \
      --code-owner-approval-required=true \
      --push-access-level=0 \
      --merge-access-level=0