First part of PostStore migration (#15123)

Automatic Merge

app/user.go

@@ -1489,7 +1489,7 @@ func (a *App) PermanentDeleteUser(user *model.User) *model.AppError {
 	}
 
 	if err := a.Srv().Store.Post().PermanentDeleteByUser(user.Id); err != nil {
-		return err
+		return model.NewAppError("PermanentDeleteUser", "app.post.permanent_delete_by_user.app_error", nil, err.Error(), http.StatusInternalServerError)
 	}
 
 	if err := a.Srv().Store.Bot().PermanentDelete(user.Id); err != nil {