created CustomPagesCourseApp class
feat: created custom pages course app plugin
created CustomPagesCourseApp class
added CUSTOM_PAGES_HELP_URL to lms and cms settings
added entry point to setup.py
feat: added toggle to ENABLE_CUSTOM_PAGES in lms and cms settings
feat: removed the option to enable/disable the availability of custom pages course apps.
Instead of hard-coding the "Learn More" and potentially other links for course
apps in the course authoring MFEs this change loads those URLs from the
django settings as part of each individual course app.
* feat: Course Apps API
This adds a new concept called course apps. These are exposed via a new
"openedx.course_app" entrypoint, which helps the LMS and studio discover such
apps and list them in a new rest api for the same.
These course apps will drive the pages and resources view in the course authoring
MFE. This system will track which apps are enabled and which are disabled. It
also allows third-party apps to be listed here by using the plugin entrypoint.
* Apply feedback from review
