Add information on managing user permissions for Libraries

[sarina]

I'm trying to update all of our docs - the docs reviewers are marking these pages as Failed, because they don't know what permissions they need. This PR adds notes to Libraries How-Tos that explain what permissions are needed to perform various actions, and also updates the page about Library user permissions to be more explicit about each permission.

[sarina]

@jswope00 this PR addresses the problems @leiramagpantay was facing with testing these pages. Could you review that the notes regarding permissions levels make sense to you, so that we can get these pages tested by a user with the proper permissions?

[jmakowski1123]

Libraries have the concept of teams, and there are 3 out-of-the-box roles on a Library Team:

-Author: Can view library content, create new library content, edit library content, use library content in courses. They can also create collections, add and remove content from collections. They can add and remove tags from content and from collections. Authors can also see who else is on the team for any library that they are an author on. Library authors are very similar roles to course staff on the course side.

-Admins: Have all the permissions of authors, but can also add and remove Library Team members. Only admins can delete entire libraries. Entire libraries can also be toggled to read-only, and only admins have the permission to switch that toggle.

-View-only: Team members who have view-only permissions on the content in a library, but who cannot create new content or edit content. View only includes the ability to search in libraries, and apply filters and sorts.

In terms of intersections with already-existing roles, if you have global admin access on the platform, you also have library admin permissions.

Library-level permissions are managed from within any given library. They are accessible via the Library sidebar, under "Manage Access". From here, admins can add or remove library team members and change the read status of the library, and any library author can see who else is on the library team.

[sarina]

@jmakowski1123 could you review this page? https://docsopenedxorg--1080.org.readthedocs.build/en/1080/educators/how-tos/course_development/add_users_to_libraries.html

[sarina]

@jmakowski1123 or @ormsbee could I get a once over on https://docsopenedxorg--1080.org.readthedocs.build/en/1080/educators/how-tos/course_development/add_users_to_libraries.html so we can proceed with testing these pages ?