Log all generated queries with log-query=full

[steve-chavez]

Problem

Currently log-query doesn't log:

• transaction-scoped-settings
• explain query whenever Prefer: count=estimated is done (ref).
• optional rollback query (ref)

Solution

Log all generated queries for log-query = full.

Implementation details

• log-query was added with some problems as mentioned on feat: log SQL query commands to stderr #3904 (comment)
• To implement this cleanly, I think we need to stop using Hasql.Snippet in our internal modules and only use it at the top level (App.hs). This would have the nice side-effect of making our query generation "pure" too.
• Then we would have something like:

  apiReq    <- ApiRequest.userApiRequest conf req body sCache
  plan      <- Plan.actionPlan iAction conf apiReq sCache
  queries   <- Statement.generateSQL plan
  -- here we can now log the queries as they would be simple `ByteString`s
  resultset <- Decoders.decode $ -- since generateSQL won't generate Hasql.Snippet, we would now need an explicit decoding step (it would be good to expose this as a new timing too)
               Query.execute queries $ -- here we now execute it with Hasql
 -- then build the response as usual

-- code simplified from https://github.com/PostgREST/postgrest/blob/d0173e71923e15b412fd459e35e1d5b97161a363/src/PostgREST/App.hs#L148-L166

• Doing the above would require a series of refactors.

[steve-chavez]

Log all generated queries for log-query = full.

Thinking more about this, to be really full we would need to also log the Schema cache queries at startup. That would need a similar treatment of "purifying" our SQL generation from Hasql too, I believe.