feature: 添加enable_any_statement选项以支持所有语法

[hanchuanchuan]

仅支持TiDB解析器可正常解析的语法.

安全上有以下强限制:

1. 用户名必须为root(无论是否开启goinception鉴权功能).因此可通过不同用户名实现权限隔离.
2. 优先级低于现有的功能开关,如禁止删表的话(enable_drop_table=false),则即可允许所有语法也无法执行删除,尽可能保证数据安全性.
3. 该功能为只读变量,不允许通过会话级进行设置

说明: 若出现语法错误(在MySQL中正常时),可创建Issue来指出该语法,以便更新SQL解析器.

[codecov]

Codecov Report

Merging #301 (1af470d) into master (80727f9) will decrease coverage by 0.0028%.
The diff coverage is 4.0000%.

@@               Coverage Diff                @@
##             master       #301        +/-   ##
================================================
- Coverage   57.8255%   57.8226%   -0.0029%     
================================================
  Files           373        373                
  Lines         73746      73760        +14     
================================================
+ Hits          42644      42650         +6     
- Misses        26648      26657         +9     
+ Partials       4454       4453         -1