Migration 54: Create configs via the config api

[dennis531]

Version
master

Describe the bug
The configs in migration 54 should be created via the config api. The current solution may not be able to read the configuration OPENCAST_DEFAULT_SERVER in the playlist migration 92 because the API doesn't konw the configuration.

[tgloeggl]

This should be resolved now since the playlist migration has been removed from migration 92 in 89bd2df

In general, the reason to NOT use the Config-API is, that it might change and break all the old migrations. It is in my opinion best to use as few APIs as possible (but of course as many as necessary) during database migrations.

[tgloeggl]

Ok, i am wiser now: We use in the plugin ALWAYS Stud.IP Core API, but not plugin API.