Postgres store include parameter

[gburgett]

The Postgres store currently doesn't support the include: parameter in find_by or find_all requests. The result of this is that a full resolution of the page can take any number of queries, as all the individual sections and their links are resolved. This is an N+1 problem.

• [ ] Support the include: parameter up to depth 3

Suggested implementation options:

• Self-joins wrapped in an imperative stored procedure https://www.postgresqltutorial.com/postgresql-self-join/
• Recursive self joins with a Common Table Expression: https://stackoverflow.com/questions/17261792/postgresql-recursive-self-join
• ?