Kessel API should provide api to create payloads for writing to table.  The API should input about a resource and return a payload that the user can write to its Outbox table. This way Kessel can control and always get a known consistent payload. 

For host-inventory to provide a valid payload for Outbox entries, I had to create the schema myself. I am sure someone else will write her schema different than what I have, which can lead to problems and waste of time.

Here is what HBI had to do
https://github.com/RedHatInsights/insights-host-inventory/blob/aa8e680084e711f671dbee26127cc855155d8f7e/app/models/schemas.py#L373-L472