Replace json_payload strategy with DockYard's json_api_assert

[begedin]

Problem

Our json_payload strategy breaks down when the view is not rendering attributes used during record creation. The reason for that is, the strategy takes a built record, infers the view from the type of record and then uses that view to build a json api payload.

If the view does not render an attribute which is usually used to create that record, then creation fails in various ways, depending on the specific case.

I was hoping ja_serializer had a convenient helper which would render a record into a json_payload using ALL attributes, and created an issue about that in the repo

vt-elixir/ja_serializer#196 (comment)

While the response was that there is no such helper, I was pointed in the direction of https://github.com/DockYard/json_api_assert, which does seem to have such a serializer.

Subtasks

• Try to use DockYard/json_api_assert to improve our json_api_payload strategy
• If that doesn't work, try the reflection route described in the linked issue

References

• Is there an easy way to serialize a record into a JSON API object with ALL attributes and relationships? vt-elixir/ja_serializer#196
• https://github.com/DockYard/json_api_assert