All Appeals list export to csv

[tovari]

Exporting App appeals from the frontend provides a csv file which has a structural issue. In the attached file, at row 402, the event_details column disappears:

https://go.ifrc.org/appeals/all?region=2

[szabozoltan69]

The reason: the bulk export is segmented to 100-row sections, and these sections are generating their CSV output independently, creating the columns "on-the-fly", depending on the content:

To fix this, we should force the CSV output to have the same structure in all cases.

[szabozoltan69]

Root cause:
event_details = EventDetailsSerializer(source="appeal.event", ...) serializes as None (not a dict) when the appeal has no linked event.