[Summer 2021] Seata extension IBM db2 support

# Background

Seata currently supports MySQL, Oracle, PostgreSQL, TIDB, etc. Seata is expected to expand more database support.

# Target

Requires reference to SEATA existing database support to implement IBM DB2.

# Difficulty

Medium

# Mentor

@a364176773
364176773@qq.com

# Output Requirements

- Support parsing DB2 common SQL to generate Undolog
- Support 2pc data rollback

# Technical Requirements

Familiar with Java programming language
Familiar with SQL used in DB2

# 背景

目前 Seata 支持的数据库有 MySQL、Oracle、PostgreSQL、TiDB等，期望 Seata 能够扩展更多的数据库支持。

## 目标

参照 Seata 已有的数据库支持实现 IBM db2 的扩展

# 难度

中等

# 导师

@a364176773
364176773@qq.com

# 产出要求

- 支持解析DB2常用增删改语句生成undolog
- 支持二阶段回滚数据

# 能力要求
熟悉Java编程语言
熟悉了解DB2常用sql

Read Seata's existing database-support implementations first and compare how they parse common SQL into undo logs and handle two-phase rollback. Implement equivalent IBM DB2 support, then verify that common insert, update, and delete statements produce undo logs and that rollback works across the two-phase flow.

Written by the indexing model from the issue text.