Guest accounts without access to sensitive settings

Currently, the only possibility to let guests access the wiki is by creating a share that is not password protected (discussed in #6620 and #6621) or by inviting them as a member. But in this case, even if they are only viewers, they have access to some settings that can be sensitive, like the member section. So if multiple guests are invited, they can each other's name.

I'm thinking about the possibility to remove access to such parts of the settings page for users with the role "viewer" or a new role "guest". This behavior could be toggled by an environment variable or on the settings page.