fix: db-pre-config function failing with pg reserved words

When db-pre-config is accidentally set to a pg reserved word
like "true", it fails with a confusing error. The function
names should be properly quoted to avoid such errors. This commit
resolves this by quoting the pre-config function name.

Signed-off-by: Taimoor Zaeem <taimoorzaeem@gmail.com>

src/PostgREST/SchemaCache/Identifiers.hs

@@ -10,6 +10,7 @@ module PostgREST.SchemaCache.Identifiers
   , dumpQi
   , escapeIdent
   , isAnyElement
+  , quoteQi
   , toQi
   , trimNullChars
   ) where
@@ -41,6 +42,10 @@ dumpQi :: QualifiedIdentifier -> Text
 dumpQi (QualifiedIdentifier s i) =
   (if T.null s then mempty else s <> ".") <> i
 
+quoteQi :: QualifiedIdentifier -> Text
+quoteQi (QualifiedIdentifier s i) =
+  (if T.null s then mempty else escapeIdent s <> ".") <> escapeIdent i
+
 -- TODO: Handle a case where the QI comes like this: "my.fav.schema"."my.identifier"
 -- Right now it only handles the schema.identifier case
 toQi :: Text -> QualifiedIdentifier