RPC returning table alias now works for pg 11/12 (#2737)

The new LATERAL query used for calling the function, introduced on
https://github.com/PostgREST/postgrest/pull/2677, failed on functions
that returned a domain like `CREATE DOMAIN projects_domain AS projects`.

Work around that by changing the query conditionally, by
obtaining a bool that represents the composite alias on the SchemaCache
and only do this on pg 11 and 12.

src/PostgREST/Plan/CallPlan.hs

@@ -17,12 +17,13 @@ import           PostgREST.SchemaCache.Proc        (ProcDescription (..),
 import Protolude
 
 data CallPlan = FunctionCall
-  { funCQi          :: QualifiedIdentifier
-  , funCParams      :: CallParams
-  , funCArgs        :: Maybe LBS.ByteString
-  , funCScalar      :: Bool
-  , funCSetOfScalar :: Bool
-  , funCReturning   :: [FieldName]
+  { funCQi                :: QualifiedIdentifier
+  , funCParams            :: CallParams
+  , funCArgs              :: Maybe LBS.ByteString
+  , funCScalar            :: Bool
+  , funCSetOfScalar       :: Bool
+  , funCRetCompositeAlias :: Bool
+  , funCReturning         :: [FieldName]
   }
 
 data CallParams