OpenCast: Improve error handling

[jrcastro2]

Expected behavior

When OpenCast event endpoint (api/events/) has state SUCCEDED but there are subformats missing we need to update the task object to failed.

Actual behavior

It keeps checking the endpoint until the subformat is there or the state is FAILED

Information about the Issue

See code here https://github.com/CERNDocumentServer/cds-videos/blob/main/cds/modules/opencast/tasks.py#L205-L236

Steps to reproduce the behavior

Not easy to reproduce, we would need to ask the webcast team to change something to have the state SUCCEDED and the encoding failing.