* Description:[fix] update sig template

* 重命名 sig/sig-template/oh-enhancement-proposal_en.md 为 sig/sig-template/oep_en.md
* 重命名 sig/sig-template/oh-enhancement-proposal_cn.md 为 sig/sig-template/oep_cn.md
* update description for create new SIG steps 
* delete graduation-criteria for english docs
* delete graduation-criteria for chinese docs
* modify sigs.json
* update user story to user scenario
* modify " 用户故事" to "用户场景" 
* update sig/sig-template/oh-enhancement-proposal_en.md. delete drawbacks.
* update sig/sig-template/oh-enhancement-proposal_cn.md. delete drawbacks.
* add openharmony sig enhancement proposal template
* update SIG english template , include goals , scope repo members 
* update SIG template, include scope and target , members  
* update SIG readme

Bug: NA
Test: NA