Populate more parameters of `generate-visualization-data` from client-payload on `repository_dispatch`

[dylanhmorris]

We should have the respository_dispatches that kick this off send a client-payload including the disease name as a key. This will be more readable and more robust than parsing the event_action string.

Originally posted by @dylanhmorris in #105 (comment)

[dylanhmorris]

Consistent with CDCgov/covid19-forecast-hub#1163