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