ReadQuery: split out to fix record field warning

The use of `where_` in DbRequestBuilder issues a warning since
GHC 9.2 as per
https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0366-no-ambiguous-field-access.rst

To disambiguate that, move the type to a separate module and use
the record field names qualified. For symmetry, MutateQuery also
gets its own module.

src/PostgREST/App.hs

@@ -82,7 +82,7 @@ import PostgREST.Request.Preferences     (PreferCount (..),
                                           PreferRepresentation (..),
                                           toAppliedHeader)
 import PostgREST.Request.QueryParams     (QueryParams (..))
-import PostgREST.Request.Types           (ReadRequest, fstFieldNames)
+import PostgREST.Request.ReadQuery       (ReadRequest, fstFieldNames)
 import PostgREST.Version                 (prettyVersion)
 import PostgREST.Workers                 (connectionWorker, listener)