Support for metadata

[felixbuenemann]

AMS allow to provide metadata, like number of total pages by passing the :meta key to render:

render json: posts, meta: { page:4, total_pages: 5 }

We could support this in postgres_ext-serializers by converting meta to JSON and selecting it as a ::json column in postgres via an additional CTE that can be joined to the final result.

Another approach would be to provide a way to generate meta data entirely in the database, which would be faster, but it would probably be harder to implement and less flexible.