Add Status feature [experimental]

[kenny-y]

• op: set_level - one of 'info', 'warning', 'error', or 'none'
• op: status - status message [experimental]

[minggangw]

I think we have implemented this feature already, please @qiuzhong confirm it, thanks!

[qiuzhong]

@minggangw , set_level has been implemented but I didn't see there is any status operation branch in the code.

[minggangw]

Oh, I misunderstood the op here. We only implemented the set_level, so let's just mark the set_level as DONE.