Update the code generator to plugin (#578)

* Update the code generator to plugin

* Fix get all tables return type

backend/plugin/code_generator/schema/gen.py

@@ -0,0 +1,13 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+from pydantic import Field
+
+from backend.common.schema import SchemaBase
+
+
+class ImportParam(SchemaBase):
+    """导入参数"""
+
+    app: str = Field(description='应用名称，用于代码生成到指定 app')
+    table_schema: str = Field(description='数据库名')
+    table_name: str = Field(description='数据库表名')