Remove unavailable recordings after being unavailable for some time

[daronco]

Recordings that are not available in the web conference server are kept in the database and marked as unavailable. This is done to prevent issues in case the server is not responding for a short time, for example.

However, keeping the unavailable recordings in the database for ever is not a good thing. If a recording is removed from the web conference server manually, for example, it will not be removed from the database and will be there until someone manually deletes it.

There could be a maximum amount of time that unavailable recordings are kept in the database before they are removed automatically. A worker could do it in background and remove recordings that were marked as unavailable e.g. 7+ days ago.