Refactor/group and role names

[tmetzl]

This pull request refactors the role and permission system to replace the "hub" scope with a more consistent "lms" (Learning Management System) scope across the codebase. It updates role, group, and permission naming conventions, and ensures all logic, APIs, and tests use the new "lms" terminology. This change improves clarity and aligns the naming with the intended application domain.

The most important changes are:

Core Role and Scope Refactoring:

• Renamed the Scope.HUB enum to Scope.LMS and updated all references to use "lms" instead of "hub" [1] [2] [3] [4].
• Updated the Role enum: replaced HUB_ADMIN with LMS_ADMIN, changed role names to use hyphens (e.g., lms-admin, course-owner, teaching-assistant), and moved COURSE_CREATOR to the LMS scope.
• Refactored group name construction and parsing in RoleAssignment, so all group names now start with lms. (e.g., lms.lms-admin, lms.course.<course_id>.<role>, lms.course.<course_id>.term.<term_id>.<role>).

API and Permission Updates:

• Updated permission enums and sets to use the "lms" scope and naming (e.g., ADD_LMS_ADMIN instead of ADD_HUB_ADMIN), and updated the role-permission mappings accordingly [1] [2] [3].
• Refactored membership API methods to use the new LMS admin and course creator roles and permissions, renaming methods and updating logic as needed.

Documentation:

• Updated README.md to reflect the new group naming conventions.

This refactor ensures a consistent and clear role/permission model throughout the codebase, making future maintenance and extension easier.