Unify optional settings documentation for REMOTE_AUTH*/SOCIAL_AUTH*

[jathanism]

Proposed Changes

Currently, the documentation for setting up default groups/permissions for remotely-authenticated users is either duplicated or spread out across the documentation for Remote User Authentication and SSO Authentication.

We should fix that and, move them to be documented to a single location and reference those docs from each authentication guide.

Justification

Currently it's not clear on whether these settings would also work with LDAP or other forms of authentication, but they absolutely should. The documentation makes it seem as if these are distinct and there are different ways. Additionally the LDAP documentation does not cover or link to these configuration settings at all.

[dgjustice]

@jathanism I'll take a look at this one.

[jathanism]

@dgjustice You're hired!

[dgjustice]

I guess this issue is a duplicate of #18