Fix deadlink in event gather pipeline docs that links to event ingestion data model

[evamaxfield]

Broken link in docs: https://councildataproject.github.io/cdp-backend/event_gather_pipeline.html

Should be updated to the renamed Event Ingestion Data Model

[tohuynh]

The generated link is https://councildataproject.github.io/cdp-backend/cdp-backend/event_data_ingestion_model.html

I think just need to remove extra cdp-backend

[evamaxfield]

Seems like it. I can also handle this if you want. I am planning on making a PR later today to do a bunch of function name + documentation cleanup and moving some functions around