fix: resource embedding opens empty transaction

This required untangling logic from App.hs.
Building/rejecting a plan no longer consumes a pool connection.

* Added io test for failed resource embedding not consuming connection
* optionalrollback to Query.hs and Response.hs
* delete Middleware module
* remove plan logic from App.hs
* remove RequestContext
* remove pkCols logic from App.hs
* remove proc logic from App.hs
* remove config logic from handleRequest

src/PostgREST/Query/QueryBuilder.hs

@@ -84,7 +84,7 @@ getSelectsJoins rr@(Node ReadPlan{nodeName=name, nodeRel=Just rel, nodeAlias=ali
   (sel:selects, joi:joins)
 
 mutatePlanToQuery :: MutatePlan -> SQL.Snippet
-mutatePlanToQuery (Insert mainQi iCols body onConflct putConditions returnings) =
+mutatePlanToQuery (Insert mainQi iCols body onConflct putConditions returnings _) =
   "WITH " <> normalizedBody body <> " " <>
   "INSERT INTO " <> SQL.sql (fromQi mainQi) <> SQL.sql (if S.null iCols then " " else "(" <> cols <> ") ") <>
   "SELECT " <> SQL.sql cols <> " " <>