(PDB-809) Store top level structured fact data as JSON

This adds the storage of the top level facts that happen to be structured in a
new column of fact_values called `value_json`. This is provided so we can query
top level facts for the /facts endpoint in a performant way, without having
to also reassemble the pieces of values into a JSON object later on.

Signed-off-by: Ken Barber <ken@bob.sh>
We've somehow changed the behavior of a query on trusted facts here. https://gist.github.com/wkalt/29c97f8e8c704e8890d6  Not sure it's a bad change but something to note.