feat: Allow filtering by IS DISTINCT FROM using the isdistinct operator

src/PostgREST/ApiRequest/QueryParams.hs

@@ -589,11 +589,13 @@ pOpExpr pSVal = do
   OpExpr boolExpr <$> pOperation
   where
     pOperation :: Parser Operation
-    pOperation = pIn <|> pIs <|> try pFts <|> try pOp <?> "operator (eq, gt, ...)"
+    pOperation = pIn <|> pIs <|> pIsDist <|> try pFts <|> try pOp <?> "operator (eq, gt, ...)"
 
     pIn = In <$> (try (string "in" *> pDelimiter) *> pListVal)
     pIs = Is <$> (try (string "is" *> pDelimiter) *> pTriVal)
 
+    pIsDist = IsDistinctFrom <$> (try (string "isdistinct" *> pDelimiter) *> pSVal)
+
     pOp = do
       opStr <- try (P.manyTill anyChar (try pDelimiter))
       op <- parseMaybe ("unknown single value operator " <> opStr) . operator $ toS opStr