Include generated query in the API

[steve-chavez]

Besides the generated query, we can also include the recommended indexes.

[steve-chavez]

I think the way to do this would be:

• Create unit tests for the PostgREST.Query.Statements module in core.
• Copy/Paste the result of the tests on the docs - which are the generated queries
• If the queries do change in core, the resulting unit tests would fail - so that would let us know when to update the docs as well.

[steve-chavez]

What I like about this:

• Increasing overall code quality - more unit tests
• If maintenance turns out to be high, it would force us to merge docs with core

[steve-chavez]

If we do the application/sql feature(mentioned in PostgREST/postgrest#2354 (comment)), unit tests would not be needed. We'd just include the application/sql output next to the request in the docs.