feat: add flat error support to config update

CHANGELOG.md

@@ -57,6 +57,10 @@
   `ConfigService`, now part of `kong.Client`) now has the response signature
   `([]byte, error)` instead of `error`. The byte slice is the config response
   body. The error is unchanged.
+- **Breaking change:** `ReloadDeclarativeRawConfig()` now requires a
+  `flattenErrors` boolean argument. When `true`, requests will include
+  `flatten_errors=1` in the query string, to activate the functionality added
+  in https://github.com/Kong/kong/pull/10161.
   [#273](https://github.com/Kong/go-kong/pull/273)
 
 ## [v0.36.0]

kong/client.go

@@ -386,15 +386,26 @@ func (c *Client) ReloadDeclarativeRawConfig(
 	ctx context.Context,
 	config io.Reader,
 	checkHash bool,
+	flattenErrors bool,
 ) ([]byte, error) {
 	type sendConfigParams struct {
-		CheckHash int `url:"check_hash"`
+		CheckHash     int `url:"check_hash"`
+		FlattenErrors int `url:"flatten_errors"`
 	}
 	var checkHashI int
 	if checkHash {
 		checkHashI = 1
 	}
-	req, err := c.NewRequest("POST", "/config", sendConfigParams{CheckHash: checkHashI}, config)
+	var flattenErrorsI int
+	if flattenErrors {
+		flattenErrorsI = 1
+	}
+	req, err := c.NewRequest(
+		"POST",
+		"/config",
+		sendConfigParams{CheckHash: checkHashI, FlattenErrors: flattenErrorsI},
+		config,
+	)
 	if err != nil {
 		return nil, fmt.Errorf("creating new HTTP request for /config: %w", err)
 	}

kong/client_test.go

@@ -279,7 +279,7 @@ func TestReloadDeclarativeRawConfig(t *testing.T) {
 			b, err := json.Marshal(tt.config)
 			require.NoError(t, err)
 
-			body, err := client.ReloadDeclarativeRawConfig(ctx, bytes.NewBuffer(b), true)
+			body, err := client.ReloadDeclarativeRawConfig(ctx, bytes.NewBuffer(b), true, true)
 			stringBody := string(body)
 			if stringBody == "" {
 				t.Errorf("wat")