Automatic merge from submit-queue

Implement first version of indexing in cacher

This PR adds a first version of indexing in cacher.

It has a really significant impact on performance - __in empty 2000-node cluster, apiserver cpu usage drops by ~75%.__

Not for 1.3, but we need this soon after 1.3 is done.

@lavalamp @mqliang @davidopp @gmarek @kubernetes/sig-scalability