Merge pull request #57259 from ericchiang/client-go-no-cache-import

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
```

Kubernetes-commit: 4a77bd53e88a719c612086df69a52899bbdd85af

vendor/github.com/gregjones/httpcache/diskcache/diskcache.go

@@ -1,61 +0,0 @@
-// Package diskcache provides an implementation of httpcache.Cache that uses the diskv package
-// to supplement an in-memory map with persistent storage
-//
-package diskcache
-
-import (
-	"bytes"
-	"crypto/md5"
-	"encoding/hex"
-	"github.com/peterbourgon/diskv"
-	"io"
-)
-
-// Cache is an implementation of httpcache.Cache that supplements the in-memory map with persistent storage
-type Cache struct {
-	d *diskv.Diskv
-}
-
-// Get returns the response corresponding to key if present
-func (c *Cache) Get(key string) (resp []byte, ok bool) {
-	key = keyToFilename(key)
-	resp, err := c.d.Read(key)
-	if err != nil {
-		return []byte{}, false
-	}
-	return resp, true
-}
-
-// Set saves a response to the cache as key
-func (c *Cache) Set(key string, resp []byte) {
-	key = keyToFilename(key)
-	c.d.WriteStream(key, bytes.NewReader(resp), true)
-}
-
-// Delete removes the response with key from the cache
-func (c *Cache) Delete(key string) {
-	key = keyToFilename(key)
-	c.d.Erase(key)
-}
-
-func keyToFilename(key string) string {
-	h := md5.New()
-	io.WriteString(h, key)
-	return hex.EncodeToString(h.Sum(nil))
-}
-
-// New returns a new Cache that will store files in basePath
-func New(basePath string) *Cache {
-	return &Cache{
-		d: diskv.New(diskv.Options{
-			BasePath:     basePath,
-			CacheSizeMax: 100 * 1024 * 1024, // 100MB
-		}),
-	}
-}
-
-// NewWithDiskv returns a new Cache using the provided Diskv as underlying
-// storage.
-func NewWithDiskv(d *diskv.Diskv) *Cache {
-	return &Cache{d}
-}