Correctly handle events like `DOWNLOAD` or `DELETE`

[JonOfUs]

https://github.com/AntennaPod/AntennaPod/issues/6957#issuecomment-2050513363

spec: https://gpoddernet.readthedocs.io/en/latest/api/reference/events.html

Nextcloud-gpodder seems to ignore the episode action type and just stores the data from the request. However, the playback position and other fields are "only valid for play”, so they should be ignored for other action types.

Maybe action types like DOWNLOAD or DELETE can be ignored completely, this depends on whether any supported clients use them.