Add auditor access for group wiki

What does this MR do and why?

Describe in detail what your merge request does and why.

Closes #354577 (closed)

Allows the auditor user to access the wiki page

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

auditor-enable-group-wiki

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Switch to the master branch and visit GitLab in your browser. Login as an admin user and attempt to visit the wiki page in a group https://gitlab.example.com/groups/<GROUP>/-/wikis/home. As an admin, you should be able to view this page.
2. Impersonate an auditor account and attempt to visit https://gitlab.example.com/groups/<GROUP>/-/wikis/home. As an auditor, you should see a 404. This is expected.
3. Switch to the auditor-enable-group-wiki branch.
4. In the address bar, attempt to visit https://gitlab.example.com/groups/<GROUP>/-/wikis/home. As an auditor, you should now be able to view this page.
5. Auditors should not be able to create a new wiki on the wiki page.

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.