Changes to Send a new user event

added Event subschema #2 to the request body allOf list

the request's body type changed from object to no type

removed the request property ab_test

removed the request property additional_data

removed the request property app_version

removed the request property dt

removed the request property event_name

removed the request property event_properties

removed the request property event_value

removed the request property initial_url

removed the request property project

removed the request property project_id

removed the request property quiz

removed the request property quiz_version

removed the request property url

removed the request property user_agent

removed the request property user_id

removed the request property user_locale

removed the request property user_time

removed the request property user_timezone

added the non-success response with the status 422

removed the non-success response with the status 400