Skip upload of CSV files that have already been uploaded

[nya-elimu]

If a CSV file has already been successfully uploaded, do not include that file in future uploads. Mark a CSV file as successfully uploaded if the server response is successful (HTTP 200...300): https://github.com/elimu-ai/webapp/tree/main/src/main/java/ai/elimu/rest/v2/analytics

This will reduce number of requests sent to the server.

Implement this in a way that does not exclude events that are added to an uploaded CSV file later the same day.

---

Depends on #116
Depends on elimu-ai/webapp#1551