Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

client-go: remove import of github.com/gregjones/httpcache

Moves NewCacheRoundTripper from `k8s.io/client-go/transport` to its own package. This prevents Kubernetes clients from requiring its dependencies.

This change removes the following transitive imports from `k8s.io/client-go/kubernetes`

```
github.com/google/btree
github.com/gregjones/httpcache
github.com/gregjones/httpcache/diskcache
github.com/peterbourgon/diskv
```


```release-note
NONE
```