MM-18089 - Custom setting type manifest documentation (#13306)

* Added custom type to manifest setting types documentation

* Update text

* Typo PR Feedback

model/manifest.go

@@ -50,6 +50,8 @@ type PluginSetting struct {
 	// "longtext" will result in a multi line string that can be typed in manually.
 	//
 	// "username" will result in a text setting that will autocomplete to a username.
+	//
+	// "custom" will result in a custom defined setting and will load the custom component registered for the Web App System Console.
 	Type string `json:"type" yaml:"type"`
 
 	// The help text to display to the user. Supports Markdown formatting.