Online Garbage Collection

[wy65701436]

1, Add http server to control registry lifecycle.
2, Add API to start/stop/enable GC for registry.
3, Add periodicity GC job into job service, consider how to show GS logs for users.
4, UI support for GC.
5, Add auto test cases.
6, Document.

[reasonerjt]

We don't think we can incorporate this in 1.6 release.
Let's clarify the scope of this story in 1.6 timeframe.

[reasonerjt]

In 1.6, we'll make verify E2E via API and remove the API from routers.