[usecase-webapi] Demo for adding pluggable step info

Impacted TCs num(approve): New 0, Update 0, Delete 1
Unit test Platform: Andriod
Unit test result summary: Pass 0, Fail 0, Blocked 0
Merge pull request #896 from JianfengXu/xujf/usecase/step

[usecase-webapi] Demo for adding pluggable step info