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:

• [x] Request and refresh current playlist from Opencast in backend not in browser as students have no write access to playlists
• [x] Perform write actions in backend to improve error handling
• [x] ~Migration flag for playlists~. Not needed, as only playlists that are assigned to an Opencast instance are considered in the cronjob (config_id)
• [x] Update oc api endpoints in migration
• [x] Cronjob: Ignore new playlists in Opencast
• [x] Remove playlist video if write permission on playlist is granted. Already implemented this way.
• [x] Add video playlist if user has write permission on playlist and video. Already implemented this way.
• [x] Should the playlist to Opencast migration be outsourced in a separate script? We'll leave it as it is for now and test it.
• [x] Should a video appear more than once in a playlist?
  • Discussion in https://github.com/opencast/opencast/issues/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[bot]]

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