feat: let model customizable (#1738)

tools/goctl/model/sql/template/tablename.go

@@ -0,0 +1,8 @@
+package template
+
+// TableName defines a template that generate the tableName method.
+const TableName = `
+func (m *default{{.upperStartCamelObject}}Model) tableName() string {
+	return m.table
+}
+`