Add wiki_access_level to group API

What does this MR do and why?

Exposes wiki_access_level for groups using the REST API.

This is both for getting and setting.

Screenshots or screen recordings

How to set up and validate locally

• Ensure you have an EE license
• Grab a list of groups from the API by hitting: http://gdk.test:3000/api/v4/groups
• Ensure the response includes the wiki_access_level attribute (if you don't get at least 1 disabled, 1 private and 1 enabled consider updating groups through the UI to check it's working as expected)
• Update a group by making a PUT request to http://gdk.test:3000/api/v4/groups/:id containing { "wiki_access_level": "private" }
• Ensure the change is reflected in the UI and JSON response
• Create a new group by making a POST request to http://gdk.test:3000/api/v4/groups containing:

  {
    "name": "Test",
    "path": "test1",
    "wiki_access_level": "private"
  }

  Ensure the group is created with the correct wiki_access_level through the UI and JSON response.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.