docs: add static test doc

[czyrye]

文档建设和优化：静态测试 https://github.com/Tencent/3TS/issues/36 issue认领。添加了StaticTest.md文档，对case_cntl.cc、sqltest.cc、sql_cntl.cc三个文件进行概述。

[tencent-adm]

All committers have signed the CLA.

[hldgs]

please transalate your pr title, pr description to english, thanks. And we recommended format to title your pr.

[hldgs]

you can use "docs: add static test doc" as your pr title