spread embeds for m2m queries

[sroboubi]

Environment

• PostgreSQL version: 14 (not relevant)
• PostgREST version: https://github.com/PostgREST/postgrest/releases/tag/v10.1.2
• Operating system: windows (not relevant)

Description of issue

I basically have the problem described in #1907
I tried using the spread operator as per #2564 and that seems to work well but:

1. it's not documented so I'm not really sure what I'm doing other than following the example. Will there be any documentation describing how it works?
2. can I do queries that filter posters using attributes of their subscribers and/or subscriptions, or sort by those attributes, etc.
3. can I use the spread operator for non-recursive m2m relations?

[steve-chavez]

@sroboubi There are docs now.

1. https://postgrest.org/en/latest/references/api/resource_embedding.html#recursive-many-to-many-disambiguation
2. Yes, https://postgrest.org/en/latest/references/api/resource_embedding.html#spread-embed