Add placeholder field and user_autocomplete type to plugin manifest (#7817)

* Add placholder field and user_autocomplete type to plugin manifest

* user_autocomplete -> username

model/manifest.go

@@ -19,6 +19,7 @@ const (
 	PLUGIN_CONFIG_TYPE_RADIO     = "radio"
 	PLUGIN_CONFIG_TYPE_DROPDOWN  = "dropdown"
 	PLUGIN_CONFIG_TYPE_GENERATED = "generated"
+	PLUGIN_CONFIG_TYPE_USERNAME  = "username"
 )
 
 type PluginOption struct {
@@ -47,6 +48,8 @@ type PluginSetting struct {
 	// of pre-defined options.
 	//
 	// "text" will result in a string setting that can be typed in manually.
+	//
+	// "username" will result in a text setting that will autocomplete to a username.
 	Type string `json:"type" yaml:"type"`
 
 	// The help text to display to the user.
@@ -55,6 +58,9 @@ type PluginSetting struct {
 	// The help text to display alongside the "Regenerate" button for settings of the "generated" type.
 	RegenerateHelpText string `json:"regenerate_help_text,omitempty" yaml:"regenerate_help_text,omitempty"`
 
+	// The placeholder to display for "text", "generated" and "username" types when blank.
+	Placeholder string `json:"placeholder" yaml:"placeholder"`
+
 	// The default value of the setting.
 	Default interface{} `json:"default" yaml:"default"`