As a CM+ I am not able to request to join a group

Problem/Motivation

When a CM or SM or admin visits a group, with the request to join a group setting enabled it gets redirected to a page with a debug message.
This is due to the fact we don't pass along the correct setting to twig which renders the ajax pop-up to request to join a group.

Steps to reproduce

Create a Closed Group
Enable "Request membership" checkbox.
As a CM or SM try to join that group
See that it fails

Proposed resolution

Make sure we pass along the correct variables in the preprocess_group so that twig knows what to render.