[Announcement] introduce and deploy reviewing and approving mechanism for `pingcap/kvproto` repo

In order to strictly control the impact of changes, especially in terms of API compatibility, we plan to introduce and deploy reviewing and approving mechanism for proto folder of pingcap/kvproto with prow OWNERS.

The mechanism is same with TiDB repo

The origin request is raised by @tonyxuqqi, thanks!

Ref GitHub pull request: