MM-21898 - Part 1: Generate and use an interface instead of *A… (#13840)

* Generate and use an interface instead of *App

app/data_retention.go

@@ -10,9 +10,9 @@ import (
 )
 
 func (a *App) GetDataRetentionPolicy() (*model.DataRetentionPolicy, *model.AppError) {
-	if a.DataRetention == nil {
+	if a.DataRetention() == nil {
 		return nil, model.NewAppError("App.GetDataRetentionPolicy", "ent.data_retention.generic.license.error", nil, "", http.StatusNotImplemented)
 	}
 
-	return a.DataRetention.GetPolicy()
+	return a.DataRetention().GetPolicy()
 }