[MM-16667] Migrate User.GetByUsername to Sync by default #11453 (#11520)

* Migrate User.GetByUsername to Sync by default #11453

* fix app errors #11453

* fix app errors #11453

* fix cmd error #11453

* fix shadow var #11453

* fix shadow user var #11453

* fix test error

* fix test error #11453

store/sqlstore/user_store.go

@@ -1009,24 +1009,20 @@ func (us SqlUserStore) GetAllUsingAuthService(authService string) ([]*model.User
 	return users, nil
 }
 
-func (us SqlUserStore) GetByUsername(username string) store.StoreChannel {
-	return store.Do(func(result *store.StoreResult) {
-		query := us.usersQuery.Where("u.Username = ?", username)
+func (us SqlUserStore) GetByUsername(username string) (*model.User, *model.AppError) {
+	query := us.usersQuery.Where("u.Username = ?", username)
 
-		queryString, args, err := query.ToSql()
-		if err != nil {
-			result.Err = model.NewAppError("SqlUserStore.GetByUsername", "store.sql_user.app_error", nil, err.Error(), http.StatusInternalServerError)
-			return
-		}
+	queryString, args, err := query.ToSql()
+	if err != nil {
+		return nil, model.NewAppError("SqlUserStore.GetByUsername", "store.sql_user.app_error", nil, err.Error(), http.StatusInternalServerError)
+	}
 
-		user := model.User{}
-		if err := us.GetReplica().SelectOne(&user, queryString, args...); err != nil {
-			result.Err = model.NewAppError("SqlUserStore.GetByUsername", "store.sql_user.get_by_username.app_error", nil, err.Error()+" -- "+queryString, http.StatusInternalServerError)
-			return
-		}
+	var user *model.User
+	if err := us.GetReplica().SelectOne(&user, queryString, args...); err != nil {
+		return nil, model.NewAppError("SqlUserStore.GetByUsername", "store.sql_user.get_by_username.app_error", nil, err.Error()+" -- "+queryString, http.StatusInternalServerError)
+	}
 
-		result.Data = &user
-	})
+	return user, nil
 }
 
 func (us SqlUserStore) GetForLogin(loginId string, allowSignInWithUsername, allowSignInWithEmail bool) (*model.User, *model.AppError) {