Add Opencast Playlists

[dennis531]

This draft pull request shows a prototype for the support of Opencast playlists. There are still some open todos and disscussion points open.

TODOs:

• Request and refresh current playlist from Opencast in backend not in browser as students have no write access to playlists
• Perform write actions in backend to improve error handling
• Migration flag for playlists. Not needed, as only playlists that are assigned to an Opencast instance are considered in the cronjob (config_id)
• Update oc api endpoints in migration
• Cronjob: Ignore new playlists in Opencast
• Remove playlist video if write permission on playlist is granted. Already implemented this way.
• Add video playlist if user has write permission on playlist and video. Already implemented this way.
• Should the playlist to Opencast migration be outsourced in a separate script? We'll leave it as it is for now and test it.
• Should a video appear more than once in a playlist?
  • Discussion in Playlist allows multiple entries of the same event opencast/opencast#5737. I will create a new issue if we have a solution and need changes.

[dennis531]

The Pull-Request for the playlists api in the opencast-php-library is still open. Thus the required version 1.6 in composer.json is not available yet.

[github-actions]

This pull request has conflicts ☹
Please resolve those so we can review the pull request.
Thanks.